You can try Helium if you aren't rooted. If you're backing up to the cloud, I think you have to get the paid version. (alternative solution, make your backups on your phone then manually transfer them to cloud storage)
Local, physical backups are a bitch on unrooted Nexus devices because OTG often doesn't work and they don't have uSD slots. Maybe someone with more experience on N5 can chime in.