I'm pretty sure it's a Safari problem (El capitan update I suppose) but I was actually getting massive lag earlier on that iPad Pro page. Upvoted you though be have you're right and your analysis is spot on.
EDIT: So the page finally loads properly, I guess for some reason it takes forever to load the images. The biggest file is a 3.5MB mp4 while all other images are under 700KB. And the loading speed doesn't change back to normal even with cache enabled. It could be some problematic static file routing and controls.
No, the problem is that the pictures take ages to load and until they have loaded, the page is completely garbled. It's the same in Safari, Chrome and Firefox.
