Yes, a lot of subforums can slow down a page, but I really don't think you have that many subforums that I can see.
Um, whoops, I just did a bit more looking around, like in this forum -
http://www.marineengine.com/boat-for...Outboard-Forum - and you have a lot of subforums listed.
However, many of those subforums only have about 50 threads each which is hardly anything. Any reason, you don't put them all into the main forum? Do you need to have them in separate forums - are the threads closed after a while or something? Is there a good reason to have them grouped as they are?