One more point, I would think with 3D touch this issue might be more noticeable: here's something which I hated and finally was able to identify: unlock 6s and as soon as home screen appeared I tried to 3d touch phone icon to make quick call, but it didn't register. So I had to 3d touch again at which point it would have been faster to just open the phone app.
But it took me a while to identify this, for a long time I just thought I wasn't pressing deep enough to do the 3d touch, it turned out iOS9 was at fault.