New iPhones have launched in late September for the last several years now. There is zero chance of the iPhone 7 coming out in January, just 4 months after the 6s. People who bought the 6s would be furious, and Apple would be depriving themselves of another 8 months of profit they could have gotten from 6s sales. It'd be like baking a fresh pie, eating a couple of slices, and throwing the rest out just to have room on your table for another pie that no one asked for.