Everything I have read online has said that the throttle body doesn't give you more power.

I don't know who told you 15 hp. Everything I seen on a throttle body change is no real gain, but its your $. Did your Roush intake requires a tune? If not its not flowing much more than the stock intake.

To give you some idea....I did Steeda CAI, Underdrive pulley, BBK TB, Bassani x-pipe with hf cats and Bassani axle backs on my 06 GT. It was then dyno tuned and I got a total of 69 hp. If you add up all the advertised gains from each individual mod I would have gotten over 100 hp, but it doesn't work that way.

^^ Yes that's a common misconception people have about mods, they see all the individual hp #'s for each mod, and add them up, and then they are disappointed when the final numbers come in. I will say though, that everything I've heard and researched shows that the TB is great addition for getting the most out of other mods.