That reminds me, I need to schedule a call with our marketing department to get our new tagline approved.
NRaas mods, proudly breaking players games since 2010! ;)
Okay, but seriously. I can understand SP being more of a mod than players will at some times be ready for. And it does add more stress to the game engine as it has so much to do, but there is supposed to be a trade-off for those using the mods specifically designed to preserve and improve game performance (Overwatch, ErrorTrap, Register, Traffic, GoHere) so that one can tolerate the extra hit and there are all kinds of controls to help dial progression back if things try to happen far too quickly.
But unfortunately this is one of its features that cannot be separated out from the rest of the mod (genetics and immigration management are other often asked for examples). Perhaps other players here know of a mod that can impact assigned parental leave without all of the other overhead. The only likely contender I can think of is AwesomeMod, but that one is much further reaching than SP is and comes with fewer user controls.
In the meantime, you may want to try the MC individual sim adjustment method whenever you notice a sim has become pregnant. How frequent an occurrence that is will of course depend on your world and playstyle.