No I've used java because it was faster for me to code something functional. There's no other specific reason.
The slowness is due to the tons of non-minified javascript loaded, to the not-yet optimized number of requests to the back-end, and also to the fact that my VPS is not a competition server.
It's actually a miracle already that it renders the way it does. I understand only now how sensitive the HN community is to these aspects, I should have understood it already I guess ... hackers like clean efficient code, and it's all good feedback.