It`s not the easiest thing to find your perfect stance. My suggestion is to just stand on your board as naturally as possible and try to angle the binding the same. When you take it on the hill the first time pay extra attention to what your feet want to do, like you may notice you wish you could angle your back foot more for example.
But no one can say your angles are correct because we don`t know if it`s comfy for you. But yeah +15,+3 is as good a start as any.