There's two main bottle necks here:

1. I made this before the scripting update for Construct 3, so everything is handled via events and tons of objects. Rewriting the whole thing via scripting would probably give it a performance boost and make the codebase much cleaner.
2. The Drawing Canvas plugin itself has poor performance at higher resolutions. It works pretty well for simple effects but if you want to draw the whole game in it it'll only work well at a low resolution. Faced a similar issue in this template which is written purely in Javascript.

I made this as a little side project for fun, but if I ever do come back to it to add features and improve perfomance it'll be to release it as a paid template.