Loading it locally I get 2s of "styles recalculated" taking almost the entire load time, in Safari's "Timeline" tool. Wrapping the main body text in a <pre>, with no other changes, drops that to 0.8s total layout time.
It's the tens of thousands of <br> tags in that block doing it, then, I guess.
Most of those are warnings like "the attribute you've used from back when HTML was slim and fast is obsolete, please use this slower modern thing instead". I doubt that's making the page slow. Only a few are actual errors.
