What OS do you have? I've got a mid 2012 macbook pro too, with only an upgrade to 8 gb ram, and it's working fine for me and my like 13 gb of cc (I have a problem whoops). Don't upgrade to Catalina, it completely drops compatibility with 32 bit games, and has been reported to not work with sims 4 in the current beta. Mojave 10.14.5 is what I currently have. I'd also suggest Clean My Mac X, helps keep everything working the way it should, and the handy mini menu at the top let's you clear ram (and view the level of ram, cpu, disk space, and more) quick and easy. Completely invaluable when it comes to trying to make sims 3 work. Up to date mono, homebrew, and in some cases Wine are all helpful when it comes to running all kinds of things too, especially if you want to try to get anything like S4PE, package searcher, mod manager, ect to work, since they're all made to exclusively work on windows (I could get Delphy's and S3PE to work with wine/mono, haven't been successful yet with any of the 4 programs besides Tray Importer and Studios which both have mac versions. Anyone have an advice I'd love to hear it!). Using Sims 4 Studio to package non script mods also makes it run endlessly faster, as well as making sure there are no spaces/symbols/anything besides numbers or letters in the name of your packages, since the game takes longer to read those slower so they load slower. Especially with twice the ram I have, and less cc, you should be good to go, good in general but especially as a help till you get a new system.
I feel you with needing an upgrade, but if you're going mac make sure you get it before Catalina becomes the standard or people come up with good workarounds for the 32/64 bit issues. Also pay attention to what all you can get to to upgrade if you want, I was so annoyed when I realized I couldn't upgrade my graphics card for this macbook. Everyone is gonna say get a PC, but I know for me mac has a lot of features that make it better for me (a photographer), aside from gaming not being the best with programmers refusing to make it work for both, so go with the brand that's going to be better for you and your needs, and then narrow down the specs you need from there. There are lists around for minimum required and suggested system levels all over, a quick google can find you one, and then compare models to see what has what you need.