[_mulder_]

Space X and Virgin Galactic are building completely different products. The only commonality is that they both go into Space (and Virgin Galactic barely even that).

SpaceX is not actually doing much in the way of 'new', to date. Their main product is an improved rocket engine design, but it's just an improvement on an existing product. (The self-landing rockets are amazingly impressive, but they haven't managed to achieve success with it yet).

Virgin Galactic is a completely new design (launching a passenger rocket plane in mid flight), at least in the non-military sector. That's a whole world of new unknowns they are having to overcome and, when you consider that, it's incredibly ambitious what they are hoping to achieve. They are less likely to achieve success as a result unfortunately. But well done for being the first to try.

The other big difference of course is money. SpaceX has way more funding behind it, and a much greater commercial potential.

[Gravityloss]

The X-15 was a rocket plane that went into space in the sixties. It was operated by the air force and NASA. I don't know if there's a big difference in the novelty compared to more traditional rockets.

[erobbins]

Slightly different requirements.. X-15 was single seat, no provision for sight seeing, trained test pilots that could handle high G forces, etc..

Also, X-15 had much more tolerance for failure, frankly. When you're doing something for the first time with military test pilots, you can be 95% reliable. Virgin has to be nearly 100%, and that last 5% is a bitch.