Some graphic chips are having major issues, my macbook pro mid 2009 didnt, it performs better.
Search the net relating to your machine and graphics card Before updating.
This improved performance on my machine:
In System Preferences go to Accessibility. Choose Display and check the box for Reduce Transparency.
This has helped some:
Guide: How to solve Yosemite memory leaks and CPU usage
https://discussions.apple.com/thread/6623697