Q: system overload on powerful macbook

Hi, I'm currently running os x Yosemite 10.10.5 on an early 2011 macbook with 16 gb of ram, and 2.7 GHz intel core i7. With one virtual drummer and 2 alchemy tracks, my system will quickly and regularly overload. My computer seems plenty powerful and I dont understand how so few things could overload it.

I have closed all other programs, adjusted every spec on audio>device settings, uninstalled and reinstalled logic, and I'm at a loss of what to do.

Sometimes when monitoring threads, some threads seem to process significantly more load than the other, but when the catch up, they overload.

Is it my OS?

I'm at a loss and it is ruining my logic experience

thank you for your help