Some common causes of lag:
- lots of items lying around (each one generates a check for hauling which adds to the queue tickover - the task isn't queued but it still takes up CPU resources figuring out no tto queue the task). This is probably the main contributor if you're on level -12, storing items in barrels or burning/selling them will help.
- large farms outputting far too many animals can give a similar issue where there are too many entities.
- too many idle townies causing a similar task queue check build-up as the first one; every tick the game checks for tasks for idle townies which again takes up resources. Ironically the best fix for this is to give them something to do: either hauling those items from the dungeons into stockpiles (to be mass-sold when the next caravan arrives) or making valuable commodities to seel to the next caravan (wooden swords work well, flowers are good for cash but the point of them is that you just harvest and leave them go so it doesn't solve your towneis' laz- I mean, idleness problems

). Basically, if you're towneis don't have anyhting to do then get them making products to seel so you can buy special gear - that stuff is expensive so you want to start saving as early as you can.
Whatever you do, make sure to do it in small stages - if you give all 50 townies an order at once then usually only about 30 will work while the others sleep, eat etc. and then around half of the hard-working townies will starve because they're working too hard. it might be best to lay off all your other projects and just concentrate on cleaning up the drops and storing your resources until you get the lag under conrol.
Hope that this is useful

What's that you're eating? A nice, juicy apple? You weren't supposed to eat that you fool, you were supposed to make it into a pie! - last words recorded words of Francis D'Avre before he went looking for snowcherries, but found a hungry Yeti instead.