Yes, maybe size is the issue on a certain kind of server. However, if one could focus in on the exact problem, and then replicate this on another system, it might really be a bug. If so, this should go into the Moodle Tracker system. So far, we don't have enough information to call it a bug.
My moodle home page still lists the course as "Course restoration in progress." I am going to assume that it is "hung" as for 15MB 8 hours should be enough time for a restoration.