While ingame, preferable paused or against a low-level bot, open the Menu(F10) and navigate Settings/Camera. Be sure that simple settings is ticked, then you will see scroll speed and camera smoothness. Lowering scroll speed will probably make you happier. Camera smootheness affects the acceleration/deceleration, makes the camera feel more 'floatty.'
For some reason, I can't seem to find the scroll speed bar when simple settings is unticked.