How to Speed Up macOS Sequoia (15)

A 16GB M2 MacBook Air shouldn’t take eight seconds to open Mail. Sequoia introduced enough new background work — iPhone Mirroring, Apple Intelligence indexing on supported Macs, redesigned window tiling — that even modern hardware can feel slower after the upgrade than it did on Sonoma.

The good news: most of the slowdown is fixable in an afternoon, and a lot of it is one-time cleanup that you won’t need to repeat.

What changed in Sequoia that affects speed

Sequoia (macOS 15) shipped with a handful of features that quietly use more disk and RAM than their Sonoma equivalents:

• iPhone Mirroring caches the mirrored display, app icons, and notification metadata under ~/Library/Group Containers/group.com.apple.iphonemirroring/. On a heavy iPhone user’s Mac that folder routinely hits 5–8GB.
• Window tiling added a new WindowServer subsystem that re-renders animations every time you drag a window near a screen edge. On Intel Macs and base-model Apple Silicon, the dragging animation can stutter until you turn the green-button hover preview off.
• Apple Intelligence (M1 and later, English locale) indexes Mail, Notes, and Messages in the background. The first 24–72 hours after enabling it pin one or two performance cores at high utilization while the index builds.
• Passwords app runs its own sync daemon that occasionally spikes CPU on launch.

Knowing where the new load comes from makes the cleanup logical instead of guesswork.

Step 1: Restart, then check Activity Monitor honestly

Before you change anything, restart the Mac and let it sit on the desktop for two minutes. Then open Activity Monitor and look at the CPU tab, sorted by % CPU. What’s at the top?

If you see mediaanalysisd chewing 80%+, that’s the Photos library re-analyzing faces and objects. It’ll finish on its own — usually overnight if the Mac is plugged in and idle.

If you see bird or cloudd working hard, that’s iCloud Drive syncing. Pause it from System Settings → iCloud while you do the rest of this guide and resume after.

If you see WindowServer consistently above 30% with nothing on screen, that’s almost always either too many displays connected or a third-party menu bar app misbehaving. Quit menu bar apps one at a time and watch the number drop.

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Step 2: Clear the iPhone Mirroring cache (Sequoia-specific)

This is new in Sequoia and almost no other guide mentions it. If you’ve ever opened iPhone Mirroring, there’s a cache directory that grows but never shrinks.

1. Quit iPhone Mirroring.app entirely (Cmd+Q, not just close window).
2. In Finder, hit Cmd+Shift+G.
3. Paste: ~/Library/Group Containers/group.com.apple.iphonemirroring/
4. Move the Caches folder inside to the Trash. macOS will rebuild what it actually needs.

On my own Mac, that recovered 6.3GB. Doing this every couple of months is reasonable.

Step 3: Trim login items and background services

Sequoia split background items into two categories: regular login items and “Allow in Background” daemons. Both eat boot time.

Go to System Settings → General → Login Items & Extensions. You’ll see two lists:

• Open at Login — apps that launch with a visible window. Disable anything you don’t actively use within five minutes of starting work.
• Allow in Background — invisible helpers (Adobe, Microsoft, Dropbox, Zoom, Logitech, Google updaters). These are the silent killers. Be ruthless. If an app doesn’t need to be running when it’s not open, turn it off.

Adobe Creative Cloud alone usually adds three or four background helpers. Microsoft AutoUpdate runs even if you only have Word installed. Dropbox Smart Sync runs continuously even when you’re not editing files.

Step 4: Check disk space and clear caches

Sequoia, like every recent macOS, gets noticeably slower below 15% free space. Open System Settings → General → Storage and look at the bar. If you’re under 50GB free on a 256GB drive, that’s your problem.

The biggest cache offenders on Sequoia in 2026:

• Xcode — ~/Library/Developer/Xcode/DerivedData/ and ~/Library/Developer/CoreSimulator/Caches/ (can be 30GB+)
• Chrome / Arc / Brave — ~/Library/Caches/Google/Chrome/, ~/Library/Caches/com.thebrowser.Browser/
• Slack — ~/Library/Application Support/Slack/Cache/ and Service Worker/
• Photos analysis — ~/Pictures/Photos Library.photoslibrary/resources/streaming-thumbnails/
• Old iOS backups — ~/Library/Application Support/MobileSync/Backup/

Clearing these manually takes about an hour if you’re careful. Quit each app first, then drag its cache folder to the trash.

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Step 5: Disable visual effects you don’t need

Sequoia’s animations are nicer than Sonoma’s, but they cost frames on lower-end Apple Silicon and any Intel Mac.

• System Settings → Accessibility → Display → turn on Reduce motion
• System Settings → Accessibility → Display → turn on Reduce transparency
• System Settings → Desktop & Dock → set Minimize windows using to “Scale effect”
• System Settings → Desktop & Dock → uncheck Animate opening applications

The Mac feels different — flatter, less bouncy — but Mission Control and app launch get noticeably snappier on anything below an M2 Pro.

Step 6: Manage Spotlight indexing

Spotlight on Sequoia indexes more aggressively than on previous versions, partly to feed Apple Intelligence search. If mds_stores is hammering the SSD, it’s a stuck or restarted index.

Force a clean re-index from Terminal:

sudo mdutil -E /

Then let it finish (a few hours on first run, much faster on subsequent). If you don’t need Spotlight to search certain folders — Xcode build directories, video project caches, downloaded ISO archives — exclude them in System Settings → Siri & Spotlight → Spotlight Privacy.

Step 7: Apple Intelligence — turn it off if you’re not using it

If you’re on a supported Mac (M1+), Apple Intelligence is opt-in but eats roughly 4GB of disk space and runs background indexing on Mail, Notes, and Messages. If you don’t actually use Writing Tools or the Siri summaries, turn it off:

System Settings → Apple Intelligence & Siri → toggle Apple Intelligence off. The model files stay cached but the daemons stop.

Step 8: Reset NVRAM/SMC if it’s an Intel Mac

Skip this if you’re on Apple Silicon — there’s no NVRAM reset on M-series chips, and the SMC equivalent resets automatically when you shut down for 30 seconds.

On Intel: shut down, hold Option+Cmd+P+R during boot until you hear the chime twice. Then shut down again, hold Shift+Control+Option+Power for 10 seconds. Release, then boot normally.

This fixes weird cases of fans running at full speed, Bluetooth misbehaving, or display brightness stuck — all of which feel like “Sequoia is slow” but are actually firmware-level confusion.

Step 9: Check for the WindowServer memory leak

A subset of Sequoia users (especially on external displays) hit a WindowServer memory leak that grows over days. Symptoms: the Mac feels fine for a few hours, then gets progressively laggier until you log out.

Diagnose: open Activity Monitor, Memory tab, search for WindowServer. If it’s above 2GB after a day of normal use, that’s the leak. The fix is logging out (Apple menu → Log Out) once a day or every other day. Apple’s mostly patched it across the 15.x point releases but a small number of multi-monitor setups still hit it.

When to give up and reinstall

If you’ve done all of the above and the Mac is still slow, three options remain:

1. Safe Mode boot to confirm it’s not a third-party kernel extension. Apple Silicon: hold the power button during startup, choose your drive while holding Shift. If Safe Mode is fast and normal mode is slow, the culprit is something you’ve installed.
2. Create a fresh user account and use it for an hour. If the new account is fast, your main user’s preferences or login items are the issue, not Sequoia itself.
3. Reinstall macOS in place — System Settings → General → Transfer or Reset → Reinstall macOS. Doesn’t touch your data; just rewrites the OS files. Takes 30 minutes and fixes a surprising amount.

A clean reinstall almost always restores Sequoia to feeling new. The reason is rarely the OS — it’s the years of accumulated state from apps, login items, and caches that the OS has to thread through every action.

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The realistic ongoing maintenance

Sequoia rewards a 20-minute monthly check-in: clear caches, audit login items, restart, glance at Activity Monitor. If you spend that time, the Mac stays fast. If you don’t, every macOS — not just Sequoia — slowly congeals.

The single biggest factor isn’t any of the steps above. It’s free disk space. Keep at least 20% of your SSD free and most of these problems never appear in the first place.