This is probably different issue, but I'm on dial up, and this forum always load slower then other sites, including other phpbb forums. It always works noticeable slower, and is seems to me that not much of the content is cached. What's the TTL for images and similar things? Maybe if TTL was increased you bandwidth usage would be lower and forum would run faster for everybody.
That's kind of the same problem. The thing is that DEVPPL it growing out of the server. I server upgrade will be made after the summer. The traffic will decrease during the summer and the site will be faster, but after that, it will need some new hardware, and that will increase the loading times aswell.