Thank you! I'm glad that you liked my music XD - I'm very good at remixing other songs but I suck at creating my own.
About the lag - After some researching I discovered that instantiating scenes and adding them as child of other nodes causes a lot of lag in the web version for some reason. And guess what? The game is constantly instantiating stuff.
But don't worry, I'll try my best to fix the lag as soon as the voting ends.