The people that committed the crimes of Nazi Germany are dead, and good riddance to them. Modern Germany is doing the right thing by commemorating their defeat. They can do that on their own terms in their own country. People don't get to just do whatever they want in Germany on the basis of being from a country that suffered under the Nazis.
Nobody is asking Nechayev to make a speech, but nobody is asking him to attend either and he still plans to do that. Nechayev described this commemoration as “part of the path to our reconciliation”, so he clearly thinks of it as something Germany should be doing in order to be friendlier with Russia despite Russia's actions
If Germany isn't doing it on its own terms then it's not Germany doing it, is it? Not only can Germany do it on its own terms, it only matters if Germany does it on its own terms.
Regardless, the responsibility Germany has does not entail giving Russia propaganda fodder for its own imperialism. That helps literally nobody.