As per this post, the problem outlined below still applies with the Bitdefender 2015 firewall:
Bitdefender on a Windows 8.1 OS (x64) PC and linking it to Server 2012 Essentials R2 - does anyone know how to allow the connector through the firewall to allow a backup to take place?
No matter what I do the backup will run incredibly slowly unless I turn off the firewall completely and use the standard Windows forewall? (e.g. 8 hours plus compared to 40 minutes)
I've tried all the options I can see but alas nothing makes and difference.