1. My 6s+ is on iOS 9.0.2
2. I use(d) my iPhone for calls, texts, emails and light web browsing. Between work and home I have access to multiple computers (including my work MBP which travels with me) 24/7, so I'm not using my phone to play games, watch TV or stream video. I love the size of my phones, but I have a 55" TV at home and I'm not going to watch stuff on my dinky sized phone when I can watch on a 55" TV.
Now, I will give you two things. At work I have a USB hub and if I stream music then I will plug the phone in. I also take my iPad with me (6th Gen) and that's what I use to watch video/TV when away from home. It's got a larger screen.
But…it's entirely possible to get the battery life I do if you do not assume that I use my phone like you do, or like a lot of people do.