I'm still running Yosemite as well. ;) So far, I just read the description. Yes, I'm not a computer newbie, but I've never done anything like that before. Plus, I like things to be as easy as possible. :P
The Sims 2 Super Collection (Version 1.2.2) from the Mac App Store takes 9,189,492,604 bytes. (9.2 GB on disk) Be aware that this doesn't include all the other data (neighborhoods, saves, ...) that will be created after you open it for the first time, but it shouldn't be more than 1 GB.