Even with a fast connection, it takes a very long time. I'm guessing the site is overloaded as the peak was a few tens of Mb/s, and generally much slower.
Some lazy loading could probably be done relatively easily where OO does on-demand load libraries, but that would significantly resource apparent in-use performance if truly done live so you'd want to background load the optional parts once the immediately needed ones are done.
I'm guessing that this is a straight compile to WASM with the minimal changes needed to things that would otherwise break completely in the different environment.
Video: https://www.infoq.com/presentations/autocad-webassembly/