Maybe not, but to just dismiss it because you hadn't heard it before is not a good idea. We've been lied to since we were in elementary school, how can anyone be so sure that this is wrong without doing any research on it?
There's a difference between questioning what you know and believing every conspiracy theory on the internet. It's not even that fine of a line.
You want to tell me thousands of German prisoners were murdered and it was covered up, I'd believe it was possible. But 9 to 15 million? That's nothing but fantasy. The sheer amount of evidence that would have to be hidden is too immense to even make it conceivably possible.