It's really, really going to depend on your work environment. In some cases, being the person who is 15% more productive buys you some leverage and slack that others don't have. Was that guy in some roles - there was definitely shit I was able to get away with that would've ended in disciplinary conversations for others.

The trick, though, is being to suss out when that's actually the case, when you're just deluding yourself , and when that might've been the case once but for whatever reason isn't anymore. That's tougher.

Your reward for being 15% more productive than everyone else is 25% extra work

Fixed.

This is only true in the kind of jobs where you're just a pair of hands.

In most jobs the more "productive" you are, the more you learn, and the quicker you progress to the next level.

While you're making money for your boss you can be learning how to make money for yourself.

On second thought, perhaps what you said is true, but that 15% premium compounds over the years.