When you start the Microsoft Skype for Business 2015 (Lync 2013) client, there's a splash screen with the waiting UI. To suppress the startup splash screen, you can follow these two steps:
Install the January 3, 2017, update (KB3141468) for Skype for Business.
Use the following GPO:
Set the DisableSplashScreen key to 1 under the following path:
HKCU\Software\Policies\Microsoft\Office\15.0\Lync\DisableSplashScreenAdditionally, to show the startup splash screen, set the DisableSplashScreen key to 0.
Note Lync 2013 was upgraded to Skype for Business in April 2015.