Hey Guys... please try the following ---> 🙂 🙂 🙂 This worked for me !!! @tomconrad helped 🙂 This should help!!! definitely mine is solved after this.. It is a workaround.. But I will keep talking to Apple folks to fix this! 😝
tomconradApr 23, 2015 11:03 PM Re: Facetime and iMessage on Macbook Pro Retina display slow after Yosemite 10.10.3 Update
Re: Facetime and iMessage on Macbook Pro Retina display slow after Yosemite 10.10.3 Updatein response to Shreyas RavindraSolved
Apple menu -> System Preferences -> Internet Accounts -> iCloud
Uncheck "Contacts"
Apple menu -> System Preferences -> Internet Accounts -> Google
Uncheck "Contacts"
etc
Open the contacts app; you should see no contacts listed (don't worry they haven't been deleted you're just not connected to the internet accounts that load them)
Now restart iMessage. It should start instantly.