It looks like you're running PHP5.6 with UBB.threads 7.7; I'd recommend switching over to PHP7, you'll notice some speed increases.
As for your homepage, I can't be sure as its not a UBB.threads page; it looks largely static except for the bit that shows the latest posts on the right; is this processed from an RSS feed created by UBB.threads, or are you performing a database query to pull those latest threads? The RSS feed option would have less of an impact as UBB.threads uses a cache for RSS feed content (it won't do a new database hit every time your homepage is loaded).
