I tried running it a few times in unity to see if something is being instantiated indefinitely, like arrows not being deleted and things like that. Everything seems fine though. Can you send me more information, please?
1. Does the game start lagging right away or only after playing for a few minutes?
2. How is the state of your run? Lots of enemies on screen? What build(INT/AGI/STR)? How many waves did you beat?