iPhone system storage 53.61GB after DFU install

I have an iPhone 6S Plus that I erased and installed clean a week ago. At this point, I've installed a few critical apps, but otherwise it is generally only used with the original system apps. However, tonight I noticed that the iPhone storage was more than half taken up, despite the fact that no music, movies, or anything has been downloaded to the phone. It is mostly just used for my work mail, iMessage, and taking pictures. I checked the iPhone storage in settings, and the System is taking up 53.61 GB.

The only thing I can think of is that there is some sort of temporary caching taking place while Photos tries to do the face scanning of my entire photo library. Does anyone have any other ideas? Could face scanning be the culprit? The phone was erased and set up as a new device, but my photos library is on iCloud, and is (I fully admit) an unreasonably large library at about ~133k photos and videos, totally 503GB on the iCloud servers... My phone is still working to scan the faces again after the clean install (also, annoying that the face data is local and not in the cloud, it had completed the entire library before the recent erase, I didn't even consider that it would have to start over on that).

Running 11.3