@Fivezenses
Roaringapps is a great site but is not official in any way, it relies on users to input data for apps and whether they work or not. I've just looked at it and TS3 was showing as not compatible in El Capitan based on one user's input. I registered and posted that it works fine for me so now the result is a draw. It is purely subjective.
As always when upgrading operating systems there is a risk that some apps won't work. TS3 running in El Capitan is working for more people than not based on user feedback I've seen not just on here but other forums and social media sites. Yes some people had to uninstall and reinstall but you don't lose your game by doing that (so long as you keep the Sims 3 folder with your user data). My game didn't work after I upgraded on my MBP but after reinstalling my Store content it was fine. After clean installing El Capitan on my iMac and installing the game it ran fine.
TS3 has always been problematic on Macs unfortunately but with some TLC it can and does run. When uninstalling it is CRUCIAL to get rid of every single residual file that the uninstaller leaves behind. Quite often people state that a new install doesn't work but there are files left over from their previous install which they weren't aware of. As soon as they have deleted those they can install successfully.