I want to acknowledge that the load-times for Figma go up linearly with the complexity of your design file + its dependencies. It is always painful when users rightfully complain about giant design files taking a while to load and fully render.
The team is working on changing that so hopefully your experience gets better over time.
This is not my area of expertise, so I am not in the position to promise anything on this forum but I just want to say that the testing framework described in the article is also used to continuously test and measure the file load/parsing time as folks are working towards algorithmic improvements.