Hi and welcome to Android Central - I would notice some fuzziness when the lighting was poor, but it didn't impact the photo quality. I would reset the device and the issue would be resolved.
Make sure there is nothing on the lense. Listen closely when you launch the camera. If you here an odd noise, you have a defective phone. It's a known issue in some GS6 that the auto focus is bad.
Resetting phone more than likely won't cause a change, it's a hardware problem, not a software problem.