KVM scaling question about compile time

Hi,

I'm running KVM on Ubuntu 14.04 server. I run a single VM with a single vcpu on the host and compile mysql source, it takes about 13 minutes. When I run 2 VMs compiling mysql source at the same time, configured with one single vcpu, it takes about 17 minutes.
Is it possible takes a less compile time when I run 2 VMs or more VMs compiling mysql?
If so, would you tell me how to do? Thank you.

Regards,
Dave