I’m having a similar issue.
Using internal hard drive.
Tried creating a blueprint or c++ project. Same problem with both
Using 4.7.3 downloaded
From my mac about box
10.10.2 (14C109)
MacBook Pro (Retina, 13-inch, Mid 2014)
3 GHz Intel Core i7
16 GB 1600 MHz DDR3
Intel Iris 1536 MB
Left it at 96% for 20 minutes both times.