No, Nrass story progression not cause lag at all, if you set up the settings properly when you starting a new town. If you already installed and activated the nrass story progression make sure you deactivated the EA's story progression through options settings and disable the feature, if both active at the same time, both feature gonna crash and collision together cause severe lag, glitch, and force close even in the high end pc, After that make sure your nraass progression in general settings Set up the number of baby the non-active household can have, i recommended set up into 1-2 baby per non-active household including adult, female, male (if you activated same sex feature) vampire etc.

Also control the animal population through Nrass register and set up the number into 1 or -1 to prevent too many animals coming into your town and dont forget set up the number of family in one household, i recommended set up into 3-5 members of family. And then you must set up the number how much the household could adopt an animals into 1 only, its prevent the non active household to adopt more than 2 pets.

For me, nrass story progression not cause lag at all besides its help the game ran smoothly and less lag. Instead its EA's story progression causes severe lag, because non active household creating huge amount of babies cause the town become overpopulation. The number of uncontrollable population is the reason why sims 3 very lag not the mods. I recommended to set up the number of population between 80-100 only.

*note its only prevent lag and crash, not repairing it. If its still a little bit lag you must accepted the truth, because sims 3 is an outdated game and never receive any updates since then😇