It's a little slow for me, but I have to say I've seen far worse.
generally whenever I see this problem it is mainly down to the hosts. Either insufficient resources, or a poorly-configured server. Assuming your installation is largely default (no major addons) then I'd have a chat to your hosts and point out the problem. vBulletin does need a fairly decent server if you want it to be *fast*. For a shared hosting plan your site is probably about the speed I'd expect...sadly.