Individual airlines will be responsible for awarding the 15,000 miles bonus to members account. oneworld states that you can only earn the bonus in one programme as they do not want to encourage those tricky mileage runners from getting 15K bonus several times. It's just one of those scare tactics that firms use to discourage customers from engaging in dodgy practices. Trust me, there are many FFP mileage runners who would engage in dodgy practices.