Yikes, that's no good. I built this game on a 10 year old HP EliteBook 8740w laptop, so I notice it chokes up in later levels as more enemies spawn in at once. But I've never experienced 2.5fps. I also notice lower performance when playing directly in the browser. Definitely try downloading this to a faster machine, would be great to get your thoughts on the game. Thanks for the review!
***Updated Oct 27, 2020***
Recently I noticed that every WebGL game I was playing using Google Chrome was giving my really bad FPS, however, things ran smoothly in FireFox. I updated Google Chrome to the latest version and WebGL games run smoother now. Hope this helps.