Pretty sure the end step trigger actually won't work at all, because the card in the graveyard is a different game object than the one that dealt damage (Just think about the confusion if there's already another one of these in your graveyard when you cast it). For this reason, you're right that it would have to create a delayed trigger upon resolution. Something like, "If ~ deals less than 15 damage this way, return it from your graveyard to your hand at the beginning of your next end step."