I don't use BC, but I do have several slim portable clients in my offices and a few Parallels VMs on my rMBP and Mini Server, all with Win 10. In my experience, I've had long install times on drives and VMs <64GB, expanding my VMs to 128GB considerably speeds up an install or update. During my upgrade/installs on 64GB VMs the upgrade/install ultimately fails 3 out of 4 times, prompting for more space - keep in mind that MS pushed a pretty large Creator's update just a few days ago, and that update could still be downloading in the background. If you're still chugging along, that could be your issue…