Why is jquery Mega Menu so slow to load?

Question

I am using jquery Mega menu and when my page loads it first shows all of the menus (including the sub menus) for a split second as it renders and then the submenus disappear and it looks like a normal horizontal men. It eventually loads and looks proper but its very distracting and looks a bit odd. I am able to replicate this on the example page above.

Its almost as its trying to hide the menu right after rendering

Does anyone know if there is a way to have this menu load "cleaner" without this jumpy incremental rendering ?