System Backup is almost useless anyway.
Make Your own copy free from vendor and mobo locking (not for OFW of course, but if You don't want CFW, maybe just install HEN?):
It is slow because You have probably hundreds of GiB to backup and PS3 have USB 2.0 ports (similar for memory cards), so You will get at best around 20MiB/s writing speed. In addition, PS3 compressing already compressed data and encrypting it. All of this taking ages.