I would wait for the 7.
Is your 6 so slow that you need to drop 6k on upgrading to practically the same thing? I have been led to believe that iPhones do not slow down at all.
What else is there?
Force touch is cool yes and useful but I probably use it once or twice a week when I remember to. Not many apps use it either. Perhaps by the launch of the 7 it will be mainstream.
Camera? The resident expert believes it to be inferior so that that as you want. I find it very good but ask yourself, will you really see the difference in pictures?
You're misinterpreting "iPhones do not slow down at all", obviously. My 5 and 5s both show signs of slowing down. However they are still very fast, and smooth. It would be better to say "iPhones stay faster for longer" [than Android].
The camera since the 6 is a disappointment, but it's still very good. Most people wouldn't see a difference.
If money is not such an issue, I would definitely go with a 6s from a 6. It's that good.