You might think that, until you see the insane rig that's used to capture these scans: https://www.uploadvr.com/meta-codec-avatars-iphone-scan/

Each scan captures dozens of terabytes of data and lasts for hours, at least for the current high resolution avatars

that's a full Debevec style light stage but you can do this stuff with a couple of dSLRs and a home lighting setup with polarised light - kind of standard photogrammetry/hq texture/normal map generation techniques.

You can see from the normal map in the video it's pretty detailed but at least for a single face capture you can do this at home. I'm not sure what secret sauce they have for capturing multiple facial expressions and some ML magic how to morph/animate between those.

Btw you can get good results with things like https://www.unrealengine.com/en-US/metahuman too

I don't see why an iPhone 15 Pro wouldn't be able to capture these scans, especially with the new "spatial video" feature, which takes a "3d" video using multiple lenses.

You'll get decent results but it won't be as good as with dSLRs and polarised studio light - if you want super detailed textures, be able to relight them etc