For the git users here (or those who want to use it): Unreal Engine creates lots of big binary files and this can be very very slow at some point. Because git compresses files.
See this link for how to tune the compression settings:
://stackoverflow/questions/12483910/fixing-up-a-git-repo-that-is-slowed-because-of-big-binary-files
I have it set to only 20 MB (yes, twenty) on my repository and check in times have improved significantly (of course, your network should be fast 
).