How to debug slow app launch

When launching my app i get the launch screen for about 2-3 seconds and only then my first UIViewController appears.

And some times my ViewDIdAppear is being called before the UIViewController is actually appearing.

I have a pretty big storyboard (15 screens).

I have some flags that i check from UserDefaults (user is logged-in ...), and i initialize crashlytics and GCM.

So the flags and the initializing doesn't seem to be the problem.

I checked system time differences and it seems to be OK.

Any ideas for debugging the slow launch?