This may work for some with massive amounts of addons, like me

note: this may only work for singleplayer, or p2p servers

While in the main menu, click on the addons tab, then click on "Disable All Addons".

When this is done, click on the small box in the upper right hand corner of gm_boreas, along with the resource pack.

If you want to use other addons, check the addons that you would like to use on the map. About 100 addons is the limit to keep up a good framerate.

When done checking the addons, click on "Enable Selected Addons" (cant remember exactly what it says).

Then simply start up a singleplayer game on gm_boreas!

Hope this helped!