I can't say for sure what your ISP are doing. But when download speed drops so dramatically ( & there's nothing obviously wrong with your LW - connection's good & you're not firewalled) it is often because of the ISP shaping bandwidth.

You haven't changed any hardware, have you? Has anything changed since LW was working well? Anything at all? What version of Java & LW are you using (in LW if you go help > about LW, it will tell you)? Have you updated to a new version of LW recently?