Overcoming random slowness with my home Wi-Fi and 2015 13″ Retina MacBook Pro
The issues aren't with upgrading to Yosemite, they're with a component of Yosemite - every Yosemite machine runs the risk of having them. The issue's been resolved in the latest version of the OS X 10.10.4 beta, which you can download by joining the Apple beta program and following the instructions to put the beta on your computer.

Here's an article explaining more about the bug in question, if you're interested.