Re: Sims 4 Lag?
I would upgrade your amount of RAM simply to "Future proof" your computer. Remember that each EP/SP/GP adds more features to the Base Game that requires more processing power and RAM helps accommodate that. You didn't mention if you had a lot of CC/Mods which also can affect your game performance.
Have you tried moving your mods/CC out of your game and seeing if that solves your lag problems?
Try this.
1) Move your Sims 4 folder to your Desktop. (Documents > Electronic Arts> Sims 4). DO NOT DELETE IT! This is where your saved games are.
2) Start up Sims 4 to allow a new folder to generate. Remember your saved games are on your Desktop and will not show up at this time.
3) Start a new game and play for about an hour to see if the game is still laggy.
Sometimes the game develops glitches and "resetting" the Sims 4 helps to solve them.