It's still early, but I ever since I got my 6S+, I have barely touched my iPad mini 2 except for work (I use it in the classroom as a teacher). Granted, this could be due to the novelty of a shiny new device and the noticeable improvement in performance, but I find the 6S+ quite suffices for the stuff I do on it, from browsing the web to watching youtube to listening to podcasts to gaming, and it has enough battery life so I don't feel like I have to outsource these activities to my iPad just to avoid having to recharge my phone ever so often.
I might go back to the iPad mini some time down the road, but I do see myself using it a lot less than what I previously did.