Thanks for sticking it out and taking the time to play the game!
I did try to tackle the lighting by baking everything into a lightmap, the only dynamic lights are 2 on the boat so hopefully shouldn't be too heavy.
I think the main culprit is probably the palm trees and the cave crystals models, I tried to use multimeshes so that they get rendered on single draw calls rather than individually, but it was my first time messing around with those and I'm not quite sure I implemented them correctly.