I have been running CS6 on my 4-year-old MacBook Pro with Maverick OS. I will replace my computer with a new MacBook Pro with Yosemite OS. Will CS6 run on Yosemite on that MacBook?
Photoshop CS6 runs fine on Yosemite, no issues with it that I've encountered, though I don't use it as much since I have CC. It's there as insurance. Your hardware isn't going affect this.
I would suggest looking at the CC 2015 update, though, because there are some really very useful speed improvements that can take advantage of the newer hardware much better than CS6 can. I realize that not everyone likes the CC option, but there's a trial that you can use and see if it makes a difference worth it to you. Even then, you can choose to save edits in a backwards compatible way for the most part, so you can create a safety net if you ultimately drop the subscription. Besides, keeping the original raw files is always a wise idea.