Do you really heat the milk and cream for 15 minutes on medium-high?

I think you're just heating the milk and cream on medium-high until it's hot, and then reducing the heat to medium for the 15 minutes of oat-steeping: "Combine the vanilla bean pod, a generous pinch of salt, homogenized milk, and heavy cream in a medium pot over medium-high heat. Once the mixture is hot, add your freshly toasted oats to the milk and let them steep 15-20 minutes over medium heat."