Skyrim: Oblivion Walker trophy/achievement?

So, I have a question about the trophy Oblivion Walker, where you have to collect 15 Daedric artifacts. As I understand, there are only 15 Daedric artifacts in total (16 with Skeleton Key, which doesn't count towards the trophy).

Well, during the quest Walking Nightmare (where everyone in Dawnstar has nightmares) you were given the choice to kill the priest, Erandur. Apparently, you had to kill him to gain the artifact from Vaermina. I didn't kill Erandur, and therefore I didn't get the artifact (Skull of Corruption). I did this quest a long time ago, so there is no way I can play it again.

I can't make a new character with the only purpose to collect these artifacts, because you need to be level 30 to play the quest Boethiah's Calling (where you collect a Daedric artifact). And I don’t feel leveling up to 30 again, it would take way too much time.

My question is, is there any other way I can get this trophy or is all hope lost?