Do Ubuntu VMs run smoothly on the MacBook Retina, 12-inch, Early 2015? I need Ubuntu 14.04 for a class I'm doing, but I didn't want to install it side-by-side. Does VirtualBox run smoothly on the MacBook (Retina, 12-inch, Early 2015)?
VirtualBox works very well with OS X as a host.  

Performance will depend on the specs of your specific MacBook, but if you are responsible with your resources (don't have every one of your apps open at the same time), you probably won't have a problem.

Certainly won't hurt to try.