Rhythm Heaven Fever lagging to the extreme on dolphin

[Creeper Of Doom]

Hello. about 2 months ago i obtained a iso of rhythm heaven fever via cleanrip from my wii u. i decided to just play it with dolphin. on the first few songs the game runs normal at 720p (with some minor stutters) but when i try Songs like Monkey watch or Air Rally. it starts to lag so bad it makes it difficult. i tried putting the resolution down to 480p and it still lags bad. i dont know why this happens because all my other games run completely fine except for rhythm heaven fever.