Steve,

If you look further, none of their tests were done at the rated maximum. They do all of their tests at 23V.
I was just trying to get the guy up and running, not trying to be exact. My experience with the 7815 is that they would get mighty hot at the rated maximum unless you had a gigantic heat sink. Yes the dropping resistor will get hot, but it will save the 7815 from overheating. I have started using switching regulators (LM2575)for my newer designs. They are more expensive, but they run much cooler and use much less power.

Regards,
Jacob