Having Origin enabled in-game has always caused issues on Macs. As well as causing lagging issues it can also cause your game to not load, something which seems to be becoming more frequent amongst players. So the best thing to do is just disable it. Unfortunately you will have to do this after each Origin update as it annoyingly enables itself each time.
- Open Origin then click on Origin > Preferences in the menu bar
- Click on Origin in-game on the right side
- If Origin is enabled in-game the button will show green. Click on it to turn it off so it looks like the picture above.
Origin now requires 10.9 Mavericks or later to run on a Mac. The Sims 4 requires 10.7.5 Lion or later. The Sims 4 will not run without Origin so technically the Sims 4 will now not run on a Mac unless it is using 10.9 or later. If you are running Lion or Mountain Lion then please take a moment to post in this thread over on the official forums.
As of 28th August 2017 Origin is only supported in versions of macOS 10.9 Mavericks and later, support for 10.7 Lion and 10.8 Mountain Lion is no longer available:
Release notes here.
If you need to update your Mac you can do so through the App Store.