Inasmuch as Prussia has been colonized by Germany - yes. St. Petersburg has been started with mainly Dutch/German influences and later got significant contributions from French/Italian architects. Czars wanted capital with European feel, particlularly its founder Peter the Great, Catherine II the Great (of German origin) and Pavel (big fan of German/ Prussian customs). Authentic Russian architecture is engraved in its mostly German fabric.
I heard a story, do not know if its true, beleive it if you wish. As the city has been neglected during Soviet times, it delapidated so much that in 1990s when some film companies needed settings showing WWII destruction in German cities - it was easier to shoot these scenes in St. Petersburg.
Due to restorations of the last about 10 years - at least facades look good.
A lot remains to be done, moreover, to keep the city of this size in good shape in this difficult climat - it needs continuos attention.
So far we have scratched the surface of the topic of historic St Petersburg center. However, if we continue, some people may get impression that nothing has been built in the city in the last 150 years. It is not true.