The first time I ever heard that term was in the movie The Hunt for Red October. That's the propulsion the sub used - and it does exist. A few years back, a prototype ferry was built in Japan that used it - it topped out at a blistering 2 (two) knots.
No, a mach 15 plane does not exist. I personally don't think there will ever be an atmospheric plane to fly over about mach 6. The SR-71 once accidentally hit about mach 4 before things started melting and its made of titanium. The space shuttle hits its max heating at something like 10,000 mph and 100,000 feet and couldn't do it for more than a couple of minute.
The point is, if you're going to get up to about 75% of orbital velocity, its self-defeating to stay in the atmosphere: you may as well go sub-orbital in space.