Earlier quoted context omitted.
I can't agree with that. Host countries share their culture through the World Cup. South Africa had vuvuzelas, Qatar put a bisht on the winning captain's shoulders, and the USA had a half-time show. Now if only it had been a good half-time show...
The difference is that they broke the fundamental rules such that 15-min half time breaks to stick a half time show in.
My interpretation is it is 15 minutes unless the referee allows something else.