Support Forum

what kind of server do you have?  shared hosting is hard with WordPress with any kind of traffic load... forums tend to exacerbate that of course because of user interaction...

there are a few topics here you might search for some ideas... not showing too many forums at once on group view, not too many topics on forum view and not showing too many posts on topic view are a few examples... but the defaults are normally fine (group view the exception since all forums are shown)...

are you using the combined css and js caches on forum - options - global settings?

how much php memory is in use?

what is taking the site so long to load?  you should probably do some analysis and see if http requests or other are slowing it down...  we have seen some strange server set ups where local gravatars (image loads) took much longer than an http request to gravatar.com...

if you saw our blog post earlier today, the upcoming 5.5 version has some db query optimizations where you could see as much as 33% fewer queries... but your problem if really taking 20 seconds to load is a much different/bigger issue than that...