C4D has an isolate button. It does. But for some reason it seems to still calculate things that are no longer visible.
In this case, isolating things to speed up a slow scene doesn’t help. Thankfully you can achieve the desired results by using layers. Here is a little tool to assist with that.
Download the tool below and throw it in your C4D scripts folder.
Once the script is in place. Run it while selecting something to hide everything but that selection.
To return to non-isolation. Select nothing and run the script again.
Hope it helps!