Hi Janku, what browser are you using? The repeat press delay is most likely a browser setting. We tested the game on Firefox, Chrome and Safari.
The upgrade system just changes the trigger chance, usually by 10% or 20% per level. I can confirm this is reflected on the tooltips as well!
Thanks for trying out our game :) I enjoyed playing as "Jole" as well lol yours was one of the very first games I've played from this year's event!