I think I will be holding on to my 6S Plus for a while. I think I have finally reached Apple fatigue as I have little desire to upgrade to any of the newer products when all is my stuff is working just fine. Newer devices will have to have killer features to get my hard earned dollar.
The 6s and the 6s+ will be mainstays for many years to come because of the 2gb ram.
If you have the 6 or worse, the 6+...Apple went to the 1gb ram well one time too many. Those two models will age quickly. The latter especially.