I highly doubt that alternate scenario would have worked if the Nazis won (for the sake of argument we believe they won even though realistically they had no chance). For me it comes down to pure economy.. there was no sustainable Nazi economy at all. It was running on credit since the Nazis took over and if they hadn't started WW2 they would have collapsed sometime in the 40s. Given that a Space Program takes up huge ressources especially in the first stages Germany would be hard pressed to finance this. It would take up valuable ressources both in money and engineering/science staff needed that could be better used elsewhere. However it is proven that given the right motivation the timeline doesn't seem unreasonable. Just look at the US after the Sputnik shock and what a big nation with ressources can accomplish if the whole nation sets their mind to it. If the US didn't roll back tremendously after the first moon landings we'd have space stations by the 90s and might be on our way to Mars by now.