I would say you should approach this as an addict would. Blood is a drug for vampires. When you feed, it's heaven for you. Imagine the agony of having blood right there, fresh supply to sate your hunger literally flowing into your mouth, and then having to restrain that? It would be hell.

If you wanted to restrict your feeding to make it last longer, I would call for a self-control roll every time. Probably also describe in vivid detail how their character torments themselves by dragging the feeding out.