I’ve got the slow down in the admin pages too when BackupWordpress is enabled. My site runs on Azure with the in-app MySQL option. The other pages run fast but that may be down to W3 Total Cache.
I’m running PHP 7 and WordPress 4.7
I notice that BackupWordpress reports the total size of the file to be backed up. It’s not scanning the file system repeatedly to update this figure, is it?