From what feedback I received over the years and my hypothesis, the following seem to be prevalent causes of lag:

• Map being open and detailed, rendering much at once.
  
• NPC logic.
  
• Map scripts.
  
• Specific troublesome addons.
  
• Sheer addon count.
  
• Having 'keep corpses' option enabled.

The first three you can't do much about (unless you make your own version of the map). The next easiest is to make sure to disable 'keep corpses' and disable some addons. You can disable all other addons and see if that leaves the performance at acceptable level. If so, you could play like that or start working out a compromise between performance and what addons to have enabled.

I list known problems in the main discussion thread here. Including addons that break things.

thanks!