So.. if your Mac seems slower at boot after updating to OS X 10.10.3 update, there is 1 quick fix that most likely will help you.
1. Turn on your mac.
2. Go to System Preferences.
3. Open Startup Disk.
4. Choose the Hard Drive that have 10.10.3 Boot, and click “Restart”.
notes: you only need to do this once after the doing the update.
Then your mac should boot faster, especially when you are on SSD 😉