Board Thread:Wiki/Forum Technical Support/@comment-25356210-20161003010736/@comment-27219153-20161003015437

While I would definitely recommend checking the amount of memory you have allocated as Deadly Forest suggested, I doubt this is the problem. In my experience lack of memory would only cause a crash, not extremely low fps.

On my old computer, whenever I launched the LOTR mod, a second java program would launch which was only visible through task manager. This 'program' would take all the cpu power it could get (99%) and also a consider amount of RAM (4GB or more). My game basicaly froze until I went to task manager and closed that program. Next time you try to play the mod, have task manager open and make sure that your CPU, RAM, and disk usage are not maxing out.

If that didn't fix your problem, take a screenshot of the pie chart in minecraft (use Shift+F3 to open the pie chart). Also a crash report may help, as its the easiest way to get a lot of information about your game and a few details about your hardware and software. You can manually trigger a crash by holding F3+C for 10 seconds while in game.