Comparing to the PRC is a bad measurement because the PRC was a state going through its demographic transition, with extremely high birth rates and mortality rates that had plunged, incidents like the Great Leap Forward notwithstanding. Germany had already mostly completed the demographic transition. Even if we assume a post-war baby boom and higher birth rate from settlers sent east (which probably won't reach the levels of a pre-demographic transition state, since the cultural ramifications of the demographic transition are essentially impossible to undo, once knowledge of intra-couple fertility control is present, as opposed to control achieved by various traditional societal methods like delaying marrying age to prevent birth rates, it is very hard to put back in the box).
No state has managed to actually reverse this and to restore birth rates equivalent to pre-demographic transition levels, with the post-war baby booms being temporary alterations that managed to push the fertility rate higher before returning to lower fertility. Even these did not achieve anything like their previous levels before the decline in birth rates happened;
(seems to be going for something about economics but this is the one I found the most quickly which does TFR, my favored measure for calculating births)
In China the total fertility rate meanwhile was... significantly, higher.
The Nazis won't be able to achieve anything like the Chinese rates as they had already gone through the demographic transition and fertility rates had fallen across the board in Germany, including in the rural regions. Those sent East can have a boost to their TFR but won't revert to pre-fertility transition TFR and only so many Germans will be sent east. There might also be negative policies since the 1970s; the Nazi Germans would presumably be extremely conservative and rigid concerning their gender policies, which has ironically tracked with poor fertility since the 1970s, as seen in the Southern European countries and Germany itself. Of course, that is also a reaction to economic and social situations which will be tremendously different in Germany, but a continual population boom driven by German natalist policies is not inevitable, and these very policies might prove to be counter-productive in the end.
I would suggest that the best equivalent we might have available of a long term developed state with a pro-natalist policy is France, which did manage an unusually high birth rate post war and continues to have a high birth rate, and for totalitarian states - much more akin to Nazi Germany - is either Communist Romania or the USSR. None of them managed to achieve growth rates of x3 or x4 times their original population. Romania was only able to increase it a few million, Russia seems to have increased its population by 50% in the RSFSR at the end of the system, similar to France. I think we should generally therefor assume German growth of, let us say, in between 50-75%. Assuming a starting population of 80 million, which was the German population in the 1939 census (might be bumped a few extra million from absorbing Alsace-Lorraine which I presume the Germans annexed in whatever scenario is under discussion and various German minorities from the rest of Europe) and we end up 120 million to 140 million.