More validation is good, however I think this will now multiple a contact's media interval by 60, whereas we already store it in seconds. So the * 60 needs to be on the 15. ... Perhaps without brackets around the (15 * 60) in my original code it was broken in the same way? ... no, as:

irb(main):039:0> nil || (15 * 60)
=> 900
irb(main):040:0> nil || 15 * 60
=> 900