I wouldn't upgrade to the 7 because you won't find many differences at all. I'd suggest upgrading to a 7 Plus or 8 at least since they've become a lot closer in price.
I would get an 8 or better. A 7 is going on 3 years old, hardly worth the money, especially coming from a 6S. Did you just buy your 6s last year at this time? If not, it makes no sense to wait all this time just to buy a phone one year ahead of what you already have and have had for quite some time.
Yes, the iPhone 7 will be supported for at least another 3 years, if not longer.
The only thing about the 7 is that the baseline storage is just 32GB. If you get the 128GB model, it is already more expensive than the 64GB iPhone 8. So If you need more than 32GB but not more than 64GB, the iPhone 8 64GB is the better deal.