I updated my iPhone 6S to iOS 10 and as always I immediately reset all settings and configure it from scratch.
However I've noticed that the call volume and the speaker volume is way lower than with iOS 9 - and I have it set up to max volume. I compared it to my father's 6s, which is still on the latest iOS 9, and the difference is quite noticeable.
Has anyone else experienced this issue since updating your 6S to iOS 10????
Honestly, I've been having the same issue. I keep my old iPhone 5s as an "iPod" (for lecture recordings, music, games, etc), and I currently use the iPhone 6. But I've only noticed lately the speaker volume quality difference between both phones, when at maximum volume level. I did, however, update my iPhone 6 to the latest iOS 10.2.1, unlike my iPhone 5s that's still at the iOS 9.1. Perhaps you guys are right about the volume difference pertaining to the iOS updates.