If it differs between 2 Lazarus, on the exact same system (both using the same WidgetSet), and the new version is "way to fast", then there may have been a bug introduced. => What was the previous version, before you upgraded to 2.0.12? (Is this Cocoa, or still Carbon?).
In any case, Tools > Options > Editor > Mouse.
=> Go to the "Wheel" tab.
You can choose between the speed "System" or "Single Line".
Depending on what causes your issue, that may help...