The closest gun I can find in Kosar to match this photo of a Matrosen Artillerie crew is the schwere Kanone 12cm M82. Kosar says though that this gun was employed by Switzerland. Did a few still find their way to the Navy? A similar gun but with a different name?
I definitely agree on "Beute" ... This Swiss website gives another photo different from Kosar on the 12cm M82, which convinces me further that is the gun. Despite the trail being significantly different. The Swiss site also cites Schneider having a hand in supplying this piece. So, I'm very much leaning in the direction of a captured Krupp 12cm M82.
I am not sure in the identity of the gun, but the Russian 152mm M1877 (42 Line Gun) does not have the cut out under the trunnions that this piece has.Also, the 152mm M77 has wooden wheel hubs, this one has steel hubs.
These are comparison photographs and drawings of the Russian 152mm M1877 (42 Line Gun):