I agree - the Waltz is a much better fit for a beginner at their wedding, however, I don't imagine they would change their song. Thank you for the link as well - it's a beautiful wedding song!
A couple who wants to learn some ballroom for their wedding is planning to dance to the song "Crazy Love" by Van Morrison. Is the slow fox-trot the best fit for that song or would there be another dance more suited for beginners?