Open Settings > General > iPhone Storage, wait for the bar to fill in, and you will usually find that Photos and a handful of apps are eating most of the drive. On an iPhone 15 or 15 Pro, the fastest wins are turning on iCloud Photos with Optimize Storage and clearing out 4K and ProRes video clips you have already backed up. The Pro models record ProRes that can hit roughly 6 GB per minute, so a few takes can swallow tens of gigabytes before you notice.

TL;DR

  • Check the real culprit first in Settings > General > iPhone Storage.
  • ProRes 4K video is enormous (around 6 GB/min); offload it to a Mac or SSD over USB-C.
  • Turn on Settings > Photos > Optimize iPhone Storage to keep full-res copies in iCloud.
  • Offload unused apps to keep their data but reclaim the binary.
  • iOS clears caches on its own, but it will not delete your saved videos for you.

What is actually using my iPhone 15 storage?

Go to Settings > General > iPhone Storage. The colored bar separates Photos, Apps, Media, System Data, and so on. On the 15 and 15 Pro the two repeat offenders are Photos (because the 48 MP main camera writes larger HEIF files and 4K video) and a couple of apps that cache aggressively, like Messages, Photos sync, and streaming apps.

If you want a deeper breakdown of where the gigabytes hide, this walkthrough covers it: /blog/iphone-storage-full-but-nothing-to-delete-whats-actually-using-it.

How do I deal with 4K and ProRes video filling the drive?

This is the single biggest issue on the Pro. ProRes records at roughly 6 GB per minute at 4K, and even standard 4K/60 is around 400 MB per minute. To find and remove the heavy clips without touching your photos, open Photos > Albums > Media Types > Videos, sort by size, and review the longest ones first.

There is a full method for this here: /blog/how-to-find-and-delete-large-videos-on-iphone-without-deleting-photos.

If you want to keep the footage, the 15 and 15 Pro have USB-C, so you can plug into a Mac or an external SSD and transfer directly. ProRes actually requires an external drive to record at the highest settings on some models, which tells you how serious the file sizes are.

How do I offload video over USB-C?

Connect the iPhone to a Mac with a USB-C cable and import through Photos or Image Capture, or plug in a USB-C SSD and use the Files app to move clips. After the transfer is verified, delete the originals on the phone and empty Photos > Albums > Recently Deleted, which holds them for 30 days. Until you empty that album, the space is not actually returned.

What should I turn on so this stops happening?

Go to Settings > Photos and choose Optimize iPhone Storage. Full-resolution originals live in iCloud while your phone keeps smaller, screen-sized versions, swapping in the original only when you open it. This is the closest thing to a permanent fix for camera-heavy users.

For apps, open Settings > General > iPhone Storage, tap an app, and choose Offload App. The app icon stays and your documents and data remain, but the app binary is removed until you reopen it.

What does iOS do natively, and where does it stop?

iOS quietly purges temporary caches when storage runs low, and it will offload unused apps automatically if you enable that setting. What it will not do is decide which of your videos, screenshots, or duplicate photos you no longer want. Those are your files, so Apple leaves them alone by design. That is exactly the gap a review tool fills: surfacing your largest clips and likely duplicates so you can decide quickly.

A note on recoverability

Deleted photos and videos sit in Recently Deleted for 30 days, so a mistake is reversible during that window. Offloaded apps lose nothing; reinstalling restores your data. Clearing app caches removes only regenerable temporary files. Nothing here is destructive as long as your iCloud Photos or computer backup is current before you start.

FAQ

How much storage does System Data use on an iPhone 15?

System Data commonly sits anywhere from 5 to 15 GB and fluctuates as iOS manages caches, logs, and Siri assets. It is largely self-managing. If it balloons much higher and stays there, a restart, then a backup-and-restore, usually brings it back down.

Can I record ProRes without filling my phone?

Yes. On Pro models you can record ProRes directly to an external USB-C SSD, which keeps the footage off internal storage entirely. For everyday clips, lowering the camera to 4K/30 in Settings > Camera > Record Video roughly halves the file size versus 4K/60.

Is it safe to delete the Other or System Data category?

You cannot delete it directly, and you should not try to. It is a mix of system caches and logs that iOS handles itself. Focus on Photos, videos, and large apps, which are the categories you actually control.

If you would rather see your biggest space hogs and duplicates in one screen instead of digging through Settings, Cleanor for iPhone scans your library and shows what is safe to remove. See the full method to free up iPhone space.