I hate people who hang out in the passing lane as much as anyone, but for those overtaking at 15 mph over the speed of the rest of traffic, allow me to explain:
The rest of us can move over a lot sooner if everyone is driving predictably at a reasonable speed for current traffic conditions.
The person overtaking at 15 mph faster than the wisdom of the crowd - that person is causing the very delays that are slowing then down.
The rest of must move slower and change lanes slower until the reckless driver is well away from us.