150cm is about 4’11”, which, while pretty short for a human, would be pretty tall for a pony. Like, I heard somewhere that an average adult pony in MLP:FiM is around 3’5” (~104CM), with Big Mac being 5’ even (~152cm). So, while it sucks that you can’t ride that coaster, try not to feel too bad about it, since most other ponies can’t either.