My computer doesn't have a CD drive but I want to speedrun this game.

Am I allowed to spoof a CD using an ISO of the original one?
EDIT: I've changed my mind about using an ISO, there is a no-cd patch that I will instead use. See: https:/​/​github.​com/​mvdhout1992/​LegoIsland2Patches/​blob/​master/​README.​md

I know the rules don't say it's not allowed, but it might create a performance advantage so I thought I would check.

No you don't have too infact I actually recommend using the iso:
https://www.speedrun.com/lego_island_2_pc/thread/0aj35/1#uioiv