If you have a brand new 2015 13" rmbp and you are experiencing ui slowdowns, there is only 1 of 2 possible reasons. 1. You setup your new rmbp as a boot from an older macbook rather than setting it up as a new macbook during the initial setup. 2. You may have faulty hardware. The Broadwell processors were delayed because of having poor yields. There is a possibility that some faulty processors made it pass screening. If you fall into possibility 1 because you set up your computer from an older macbook, you should reinstall Yosemite from scratch by doing a command+R on bootup, deleting your drive and reinstalling OS X. If you fall into possibility 2. You should consider returning your rmbp and trading it for a new one within your return window. If you try to create a "fix" for your laptop by following someones advice about resetting pram or something else and it temporarily fixes your macbook, you may have the issue come back later when you are not in the return window. In the end its up to you, but you invest a lot of money buying a laptop. Make sure it is everything you want it to be.