The original Space Jam (1996) site does this for navigation (and it still works fine): https://www.spacejam.com/1996/cmp/jamcentral/jamcentralframe...
edit to add: And this makes a large part of the load time (when not cached). Other than that, the largest part is the SSL handshake and the fact that the server seems to be a bit slow (WRT the fact that it serves static content; 200ms for dynamic stuff would be okay).
Still a lot faster than most of todays websites.