I, too, found the latest version of Fusion to be brutally slow, so much that I will check once to see if there is any way of speeding it up. If not then I will be asking for a refund because it is unusable.
My system:
early 2009 MBP
8GB RAM
El Capitan
The WinXP VM was migrated from Parallels. I don't have my disk to reinstall WinXP from scratch (it's across the country)
I have tried a variety of config settings. 1/2 CPU. Various amounts of RAM. There are no run-away processes.
If someone would like to suggest some optimal settings I will give it a go and see what happens.