O-U-C-H!
I mean, I agree that Unholy needed something to tuned down.
But I also feel that is a very steep nerf especially since the Mastery changed in Shadowlands. Will this mean we will see Haste and Versatility move up on the stat priority?
Will the Eternal Hunger:
(Dark Transformation's duration is increased by 3 sec and your Minion damage is increased by 3.0%)
Potency Conduit become even more important to get?
Overall I believe Unholy will be fine and still be "upper tier" DPS in raids and M+ but... 15%... jeeeeeeeeeeeze.