I just compared the 6, 6S, and 6S+. The 6S+ is the worst of them all. I also noticed that the camera is better on the 6S than the 6S+!!! The pictures are supposed to be much better because the OIS!!! I can't stand that I find these little things that bother the **** out of me.
The speakers are much different. The 6 has the best speaker out of the 3. It is very loud, clear, and crispy. The 6S sounds crispy but not nearly as loud. the 6S+ sounds HORRID! The trebel is gone and there is no bass on either of the 6S' now compared to the 6. I am a music producer and engineer and knew right away that there was a difference. This is so ridiculous. And, the camera BS is ridiculous too. There's nothing better about the 6S+ camera at all because it's worse. I'm disgusted...
Not to mention when you hold down the home button there is no more beep (which I know they swithed to a nice subtle vibration) and no more vibration! My 6 still vibrates when you hold down the home button to launch Siri, but not on the 6S'. I talked to Apple and they admitted it was an issue that they are hoping to fix in the next update (9.0.2) which they didn't do... I feel like Apple rushed this phone out and didn't pay attention to quality this time. It is horse sh*t.