I have a similar problem. (MB Pro, early 2013 16GB RAM, 750 GB SSD)
If I run one VM it usually runs acceptably for a few hours up to a week. If I run 2+ VM's, it runs for a few hours to a couple days. After that time period it really slows down. The graphics are laggy and HDD access seems to be really slow. The CPU gets pegged just opening an application. No interrupt storm as on the iMacs.
Swapping to V10 helps somewhat but it always ends in the same condition. The only way to rectify it is to close all VM's and shut down vmware. Once I restart all is good again for a while. Shutting down a slow VM can take 10-15 minutes instead of 1 or 2.
It's really frustrating.