Second Daughter is fifteen months old today and she's still nursing. First Son weaned himself just a few days shy of fourteen months. I weaned First Daughter completely by the time she was thirteen months old. Second Daughter has shown no signs of giving it up. Though she only nurses a couple of times during the day (before nap, before bed), she still nurses quite a few times at night. I've never nursed a fifteen-month-old before.
It seems very much the same as nursing a twelve-month-old.