I should have mentioned that while that book is the current one, its also out of date and isn't their current practices.
I've heard of people injuring themselves by starting dynamic dilation before Dr Suporn said to start, so you'd want to be careful. It said to be quite an aggressive technique.
Perhaps someone else might like to say something, but I don't think its really 15 minutes. Maybe 15 minutes after half an hour of getting to depth, repeated with a larger dilator, plus 10 minutes on both ends to prepare and clean up...