Restoring an iphone backup

I have lost my iphone 6 (64gb), but I had a backup saved in itunes on my mac (the size of the backup ~15gb). Over the weekend I bought a new Iphone 6 with only 16gb of memory. So now when I try to restore my backup, I get an error message saying "not enough space". What should i do? is there any option to breakdown that backup. I obviously dont need to restore everything.

Thanks,

Nikita