[ubuntu] Ubuntu running slow on VM after enabling 3D acceleration?

So Ubuntu 14.04 (x64) was running extremely slow at first when running it in Virtual Box. I enabled 3D acceleration but it's still running slow, especially in fullscreen mode.

Here is a list of the settings I've set:

Base memory: 2 GB
Processors: 2
Video memory: 128 MB


Should I increase the memory in order to make it run faster, or is there a better solution to the problem?