30% overhead is often a function of team size, not methodology. A team of 30 is not likely to be agile in a meaningful sense, there are too many coordination vectors and communication channels.

And if those in a position to ask about the rest of the team aren't sold on agile to begin with, the odds of it working are inversely proportional to the odds of people just going through the motions while fearing for their jobs and polishing their resume for a year.