Chosen Solution

My iPhone 6 camera is having some problems and I am going to visit my nearest iPhone repair shop. But then I was hoping if I could ask the shop to swap my iPhone 6’s rear camera (i.e. 8MP) with that of the iPhone 6S’s rear camera (12MP). can it be done?

No unfortunately. The 6 camera and the 6s camera have different pinouts and cable shapes preventing them from being interchangable. Sorry about that!