Site can't handle large volumes of data and is extremely slow and laggy

The concourse site is dreadfully slow and when we opened a ticket to understand the issue, we were told it was the volume of milestones, tasks, subtasks on the site that was causing the lag and slowness. Concourse needs to be able to handle a high volume of milestones, taks, and subtasks, without slowing down otherwise, what is the point. We actually have a fairly reasonable number based on a normal workplan so the fact that the system can't handle it almost makes is useless.