You might be one of the unlucky many who’ve been issued a faulty iPhone. A small component in some iPhone 6 Plus phones, sold between September 2014 and January 2015, is causing the iSight camera to fail. If your phone falls in a certain serial number, you’re due for a new one. Check with Apple if you qualify.
My camera broke 1 month ago. It wouldn’t focus to object afar, unless I point the camera upwards, tap it with my fingernail, and point it at the target. If I let it focus onto anything close, it would get stuck again. It felt like a mechanic failure.
I brought it to the Genius Bar and described the issue, and they replaced the camera for me within an hour. Since the phone was still within the warranty, there was no hassle.
This is my plain and bland experience, just for your reference. And btw, my serial number is in the affected batch.