I have 2*12TB whitelabel WD drives (harvested from external drives but Datacenter drives accourding to the SN) and one 16 TB Toshiba white-label (purchased directly also meant for datacenters) in a raidz1.

How full is your pool? I have about 2/3rds full which impacts scrubbing I think. I also frequently access the pool which delays scrubbing.