Include KB3102812 (Slow "Checking for updates" fix) and KB3138615 (Windows Update Agent) as a pre-req on Windows Server 2012 R2
As can be seen here: https://serverfault.com/a/840872 The Windows Server 2012 R2 get stuck when searching for updates without Server 2012 R2 and KB3138615 - This is the Windows Update Client (Agent) March 2016 update, that doesn't seem to be a Windows Update pre-req as WSUS Offline Update didn't downloaded/installed it. More info about this update can be found here: https://support.microsoft.com/en-us/topic/windows-update-client-for-windows-8-1-and-windows-server-2012-r2-march-2016-758f2099-93d8-a2ae-a1fb-b8e75b9a4cb2
The update KB3102812 should also be a pre-req as Windows Update update check is slow and have a high CPU usage, as can be seen here: https://superuser.com/a/1189745/174557 More info about this update can be found here: https://support.microsoft.com/en-us/topic/installing-and-searching-for-updates-is-slow-and-high-cpu-usage-occurs-in-windows-8-1-and-windows-server-2012-r2-f8231dba-ddcd-8ce7-e3aa-0f4d9051fd69