My quiz backups (2.6.1) are usually about the same size (30 MB), without users data. These are math or physics quizzes, 30 questions each, with several pictures. I do resize my pictures to the least acceptable size for display before uploading them, they might be about 50kb each. One quiz might have 15 such pictures in it. In 1.9, I had noticed that I had the choice whether to "include course file", and I needed to include them, because pictures linked in quiz questions were "course files"; but, either all of the course files (= pictures in my case) were included or none, not only those that were linked in the quiz being backupped. I used to ascribe the size of backups to that fact. Now, in 2.6 files are managed differently and I haven't yet understood rightly how things work, but backups are still about the same size, so I assumed that all the picture files, from all quizzes in the course, are included in the backup also in 2.6. I don't kow for sure and would be glad to hear from others usres if it is so (which would seem somewhat of a waste?).
Giancarlo De Pol