Same environment: KM 8.2.4 on macOS 10.14.5. Before the test the KM Engine was using 1.10GB of memory, which does seem higher than I would expect, but enabling and disabling my biggest macro group containing 187 macros was instantaneous no matter how many times I did it and seemingly had no effect at all on how much memory the KM Engine used.
I will say that I did actually notice the KM Engine taking up around 5GB of memory sometime in the last few weeks, but in my experience, that is very unusual. I've been using KM for maybe 7-8 years at this point and I can count the number of times that sort of excessive memory usage has happened on one hand, so I don't think it's normal or expected behavior.