So with MQ2Map loaded the map in FM will have tons of mobs, opening the map will often cause lag the first time you open it in a zone, and anytime you drag the map around. You can type /mapfilter npc to temporarily disable the displaying of NPCs on the map, click the "labels" button, and then /mapfilter npc again to turn the NPC's back on.
You can also produce the described behavior by having too much text visible on screen in the chat windows by having a bunch of chat windows that span from the top of your display to the bottom. I've encountered this using 3440x1440 resolution and opening probably 5-6 chat windows, with one of my plugin windows stretched from the top of the screen to the bottom. You can solve that by making the windows shorter, or closing additional chat windows that you don't really need.
It's more common that the issue is with MQ2Map trying to show a label for every creature in the zone, and FM has a TON of creatures, so it's very common it happens there.