I have a iPhone 6s Plus, 64gb, and I love it. I did not upgrade to the 7, because the specs sheet is quite similar.
iOS 10 seriously isn't using that 3GB in full, and the 6s+ has enough ram.
Not upgrading is just holding yourself back. iOS10 has a few things I am visually not too happy about, and there are some obvious silly bugs that make it feel like a beta for that one second it frustrates me. But, I am glad I upgraded regardless.
I run the beta and the final on this phone, with pleasure.
Don't forget, the 6s+ is a beast, it is very powerful basically, and it's not like you have a 5 at 32bit that goes from iOS 7 to iOS10 and you have to live with a tiny bit of performance compromise. You have a full fledged 64bit macine that runs iOS 8->11 just fine.