You can make 15% selling toothpaste. Further, a billion dollars won't even get you started. The R & D alone would cost many times that.
Imagine yourself sitting in front of the board of directors proposing to put all of the assets of the company on the line for a 15% profit if you succeed. Now imagine convincing a bunch of bankers to finance this project.
Boeing is having some dificulties getting financing for its next generation passenger jumbo jet because of the huge costs. There is simply no company which can or would take this kind of risk.