That would depend on how many apps you have running .. It could be completely normal if your phone is working hard to keep up with them.
Is it normal for your iPhone 6s which is charged up to 100 % and then after 3 hours it s down to 40% . But you use it for the whole 3 hours?
Yep. If you want it to last longer you can ethier put it on airoplane mode (no internet though) or decreese the brightness.