OS X El Capitan: If Time Machine is slow
Try these suggestions if Time Machine is slow.
The first time you use Time Machine, set it up in the evening so that the initial backup can be done overnight.
If your backup disk is a Time Capsule, leave your Mac in the same room as the Time Capsule for the initial backup, or use an Ethernet cable to connect your Mac to one of the Ethernet ports on the Time Capsule.
Virus scanning software can make Time Machine backups very slow. If you use Norton AntiVirus or a similar product, try to exclude your backup disk from automatic scanning. Also make sure you are running the latest version of the virus scanning software.