According to Nerdist...
George Miller, who tells EW that the idea for the film came to him back in 2000. Apparently, that idea involves one long, sustained chase: “I wanted to tell a linear story–a chase that starts as the movie begins and continues for 110 minutes,” with the piece promising largely practical effects and a dialog-light script.
Late last year, MovieHole reported on the film's delayed release...
Miller, who has been trying to bring ‘Mad Max’ to screens since Tina Turner retired from the cage-shouting business, says they also decided to bring it out in 2015 so they wouldn’t have to compete against the World Cup.
MadMax 4 Production