I'm curious, why is that just two thousand comments would bog down the server? What kind of processing is done by the server to render a thread?
That mammoth thread at least tells us where the brick wall is: at about two 'who is hiring's.
If it’s significant then you could ship the UTC posting time to the client & calculate the displayed value in Javascript & eliminate that particular part of the load at least, which in turn might enable more caching internally.
(You’ve probably looked at this already though.)