trust me....
15's are the way to go.
research shows FREQUENCY of a message is what is most effective.
and you can run more 15's for the same price as a few 60's
if you think you can "get more message" out of a 60"...
that may be true on the surface,
but look at it from the LISTENER's point of view.
1- if you cant convince them in the first few seconds, you've lost their interest.
2- (again, thinking like a listener) would you rather listen to a quick 15-minute pep talk, or an hour long speech?
as for the Clear Channel "less is more" idea...
it was created to cut down on the length of commercial breaks.
(again...short, sweet, and to the point)