I have high end computer (i7-7700 with 32GB of empty RAM) with pretty good graphics card (GeForce GTX 1060)... and this site is lagging. I can't even scroll properly.
Most likely suspect is the typewriter animation, which ought to be done with https://github.com/tameemsafi/typewriterjs (but maybe it's just how they used it - or maybe something entirely different, I just had a quick look).