Dumb question, but when you invoke the app switcher using 3D touch (pressing on the left edge of the screen), is the device supposed to vibrate? My 6s doesn't seem to. Seems weird that it vibrates almost everywhere else 3d touch is used.
Mine will give one single "click" of the taptic engine right as the app switcher opens up. The same "click" that it gives when I go to use 3D touch on an app on the home screen and the list of shortcuts pops up. Not that it should matter, but using iPhone 6S 128GB with iOS 9.1.
I find this gesture hard to invoke without going back in that app or touching something within that app so I don't use it. Might be because of my Otterbox case though.
So if you press and swipe right you don't. If you press, and then release the press some (don't come off the screen) and then press harder, it will give haptic feedback and the app switcher will open fully without needing to swipe right.