The pump is really what makes the AIOs loud and the H115i and the H100i will have the same pump. 140mm fans will be quieter than a 120mm fan because they can spin slower while moving the same amount of air. But sound is not linear, so if you have a pump that is 30db and fans that are 25db, you don't get 55db when they are together. I would probably be closer to 33db. So you really have to look at the loudest component (which is the pump) and everything else is secondary.
I have a H115i on my gaming rig and it is not too loud, but it really depends on the case though. If you have a quality case, it will dampen the noise. But if you have a cheaper case, then it will be louder. Swapping out the fans that come with the H115i will...