Pixelation and line artifacts in iPhone 15 camera photos

I would say you probably have intermittent hardware failure on your camera sensor.

You could pre-empt an Apple repair shop visit by backing up, erasing the phone and setting up from scratch (no backup) and see if it still does it.

If you have a Mac you could create a backup on that and archive it. If you use iCloud

backup, turn it off as soon as you set up the phone again.

There is some risk so ensure you learn how to perform this.

Back up iPhone - Apple Support

Erase iPhone - Apple Support

Set up your iPhone or iPad – Apple Support (UK)

With that new information you may be right. However as this seems to be your phone only, I would still go through the process of setting up as a vanilla device and see if that stops it, to eliminate any of your apps.

I hope you are fully signed up to iCloud photos etc as it makes it a lot easier to set up again from scratch.

Add back your favourite apps as you need them.

If you have mac update the phone to the next iOs when released in Finder so you replace the whole firmware.