I had a bit of a panic induced call from a former client this morning because it took to long time to wipe a device from SCCM. Luckily there is a hotfix for this.
He applied it and … as if my magic, the issue went away, we were unable to test this on Android devices, but his iOS and Windows 8.1 devices were all wiping a lot faster.
To apply this hotfix, you must have CU3 for System Center 2012 R2 Configuration Manager installed.
You do not have to restart the computer after you apply this hotfix.
Hotfix can be found here http://support2.microsoft.com/kb/2990658/en-us