Didn't have that problem with 14.10 but on a fresh install of 15.04 (Asus N550JV), I found the scrolling button WAY too sensitive.
With the touchpad actived or deactivated, it makes no difference, scrolling precisely with the mouse is awful and just impossible. The mouse is a Logitech M560. It is a few months old and had no trouble on 14.10 and doesn't have any trouble either on W8 (dual boot).
I checked the system settings but there is nothing to set the mouse scrolling speed (but there is a slider for the mouse double click speed and another one for the cursor speed on the touchpad).
Any help appreciated, thank you guys.
Eric