You can check inside the skin folder yourself to see if there are large images and what not. Some skins can just perform better than others. I don't have the skin, so I can't check myself.
If you switch back to whatever the original skin was and you are no longer having issues, then it's probably the skin... Not really sure what else to tell you in that case.
If you just noticed your performance go down a bit in general (i.e. switching back does not change anything), restart your computer, close other things you have running in the background. Try the other things on this wiki page:
help/wiki/Performance_Troubleshooting