I have a 6 and just got a 6S in last week. I'm returning it. The extra RAM does not affect my usage and the camera is not what I'd call a vast improvement. Live Photos and the front facing camera flash are software upgrades and should have been part of iOS 9 for iPhone 6 users at least, but they're gimmicks to me. I've not yet seen force touch to be worthwhile. Hoping the 7 is a worthwhile upgrade this fall, otherwise I'll keep my 6 for another year. I did the same with the iPhone 4; didn't get another iPhone until the 5S.
I also purchased the 6S Plus and played with it for about 12 days before deciding to return it for a full-priced refund. The added gimmicks do not justify spending the $949 for the latest & greatest... The extra RAM was noticeable, but because I had the "Samsung" processor (not the more efficient alternative which was in some), my battery life was horrible, compared to my 6 PLUS. I am happy abou the return and will await the 7 PLUS!