I use a combination of two mods to help with sim autonomy problems in the game.
The first is Turbodrivers simulation unclogger, which can help with problems wherein sims are locking up in a frozen state. Available
here.
And coolspear's Quicker Sim Autonomy & Simulation Lag Improvements, which just tweaks tuning related to autonomy for a smoother overall autonomy experience. Available
here.
Both mods still work with the most recent update without any issues and are fully compatible with each other. Using them both, I usually have no simulation lag in my game even with maximum sims on lot set to 50 in MCCC and on the largest lots. (I say usually, because I had a little bit in a 64 x 64 lot with a TON of skill and entertainment objects after I had placed 2 copies of every single skill book on the floor. Until NPC sims had put away most of the books into bookshelves, that lot lagged a bit... :lol:)
That said, I voted for moving to a smaller lot. I find 64 x 64 just to be much too large for a played sim household. It's too big to feel cozy and homey...not to mention you can put, literally, everything you could ever desire on the lot, and I prefer to have incentive to visit other locations. My sims travel to "do things" pretty much every day, and I enjoy that.