Oh, absolutely. It's definitely a step in the right direction. I'm coming from the 6+ as well. Had Apple done things correctly the first time around, I'd probably still have my 6+, but the performance was so frustrating.The 6+ was massively inferior to the i6 and I should imagine that the 6S+ is inferior to the 6S, although to a much smaller degree. The 5.5" HD display coupled with the downscaling involved to render content will undoubtedly lead to some downturn in performance. However, having come to the 6S+ from the 6+ I am completely happy with it and experience zero 'issues' when it comes to the hardware.
If I compared my phone to a 6S then I may see some differences but as I'm not going to be doing that, and considering that my phone performs splendidly then I'm a happy camper.
I should've specified that everything else in the 6s+ UI is on-par with the 6s, at least from my tests. It's really only the 3D Touch menus where I noticed a difference. Turn-on reduce transparency, and you can definitely see a difference. That's how the 6s performed. Honestly, I think it has to do with Metal handling the blur effects. In benchmarks, Metal is often behind OpenGL by 15-20 fps. I think once it's optimized a bit more, we should see an improvement.
It comes down to screen size, and battery life. If you want the larger screen, and the AMAZING battery life, go with the 6s+. If easy one-handed use is important, and you don't mind charging your phone, go with the 6s. Both are absolutely great phones.