It' s a method I've used a lot too but it's a good idea to have some kind of idea of the basic pitch power settings in any jet. You wouldn't just rotate and wait to see what speed you ended up with would you? No, you go for 15 degrees cause you already know it's close to what you're gonna need. T.L.A.R is doing it the hard way mate, something I'll save for arsing about down route. I have a sim check for job and I've never flown 747 before......