Use me as a data point, those of you considering "upgrading."
I tried both. I stayed with the 6 Plus. Reasons: weight and absence of features that I found annoying (force touch). Plus, I did not find the 6S Plus appreciably faster for most of what I do on a daily basis, which surprised me. The speed was the thing I was most looking forward to, and I thought it would tempt me to ditch the 6 Plus. The small additional weight of the 6S Plus was just enough to make the device annoyingly and noticeably heavy.
So I bought a new leather case on eBay for my 6 Plus, and I'm loving it more than ever.
I tried both. I stayed with the 6 Plus. Reasons: weight and absence of features that I found annoying (force touch). Plus, I did not find the 6S Plus appreciably faster for most of what I do on a daily basis, which surprised me. The speed was the thing I was most looking forward to, and I thought it would tempt me to ditch the 6 Plus. The small additional weight of the 6S Plus was just enough to make the device annoyingly and noticeably heavy.
So I bought a new leather case on eBay for my 6 Plus, and I'm loving it more than ever.