Backup is to create a new GHO file, and one-click recovery is to load a GHO file.
GHO is equivalent to a highly compressed image file, but 15G is absolutely abnormal. A GHO image of win7 flagship version is 1 to 2G, plus the software added by pirated CD manufacturers. Is there too much stuff on your C drive?
If you want to back up:
You download another one-click ghost software and back it up again.
If you want to restore:
Then go online and find a cam-to download, and there will be GHO files in it.