If you install the SP base mod and activate its story progression, then there will be no emigration of resident sims. It is totally off by default. You get an offer to switch SP's progression on when the game starts up the first time a world "sees" the mod, but this can be checked at any time after startup or within gameplay.
On City Hall or an in-game computer, NRaas > SP > General Options > Enable Progression > (you want True)
If Enable Progression is on False, and you have story progression checked off on the built-in game options, then EA's story progression is in control. It doesn't matter which way the game option is set if SP's Enable Progression is True.
NRaas mods that are entirely or mostly designed to improve performance: Overwatch, ErrorTrap, Register, Traffic, to an extent GoHere. A MasterController Reset Everything, run from the Town menu on City Hall, is also advisable every few sim weeks or so for most worlds. MC Resets are intrusive to gameplay and can take a good 10-15 minutes to run depending on the size of the world, but they should never do any harm.
Maybe this page will help further?
http://nraas.wikispaces.com/Tips%20For%20Better%20Game%20Performance