boot very slow after installed Yosemite

I had a similar problem on my Macbook Pro 2014 after downloading Yosemite. It took more than 1 min to boot up. I went to Apple support center in Kl and they told me yor macbook is not in garantty anymore and it takes about 2-4 weeks to check your macbook and we will charge you. However, I followed first comment of this topic but it didn't work. But I got idea and presses commoand+option+P+R (all key one time) after that my system meseeage me to reinstall the Yosemite, I click in it and after arround 6 houres the software was downloaded and updated and furtunatly my problem was solved. hope this way can solve your problem also.

This process erased your information from your mac?

Thank you!

My MBP is an early 2015 model. Since upgrading to 10.10.4 and 10.10.5 I have noticed the startup is far slower than normal. After power on, the screen remains dark for much longer.

I followed your instructions and it's back to the (almost) instantaneous start up when I first switched it on.

No I didn't loose any information

Best solution for now is clean reinstall Yosemite. I had Mavericks and it boot up for 20 sec. (iMac 21" mid2011). After upgrading to Yosemite through AppStore my mac boot for 1.5 min. I made clean reinstall of Yosemite (with formatting) and ... voila... 30-35 sec. Also overall system speed increased too/ So don't hesitate, just do it. And don't forget to backup all your persolan files as well as you formatting.

i was having the same issue, i did the PRAM reset now it's fine 🙂