I would be shocked if the camera is any better than the camera of the iphone 6. 12 megapixels is just a little more resolution, but nothing major. The lens hasn't changed, and no optical image stabilization. The iphone 6 can already record 4k fine. I'm pretty surprised that apple rested on their laurels here for the camera, because the S6 and G4 are much better hardware wise and I don't think Apple kept up this time .
No reason at all to buy the iphone 6s at the pricepoint that Apple wants. Force touch is just a right click. 99% of what you can do with force touch can be done simply by press-and-hold functionality. It's not a big deal.
Battery life won't be any better, if not worse. Processor may be a bit faster but nothing major either.
Looks like the iPhone 7 will be the true upgrade next time: thinner, much faster, much better camera.