Grainy photos with iPhone 15 Pro

I spent 1 hour on the phone with technical service before being sent to the Apple store. Was there from 3:30 yesterday until 7:10. Reloaded software and put in a new camera. Same problem: grainy photos! Spending way too much time trying to fix an expensive phone that isn't working. Also, got a defective cord from Apple which meant my phone didn't turn on at all and that took an hour of technical service to find out the problem. Very frustrating!!