The 22.5 cm Minenwerfer M 15 was a heavy mortar used by Austria-Hungary in World War I. It was developed by Böhler as an alternative to the German Ehrhardt 25 cm schwere Minenwerfer which Böhler was having problems building under license. It was a muzzle-loading, smooth-bore mortar that had no recoil system whatsoever. The entire mortar had to be levered around to aim at new targets. It was not particularly accurate and bombs often fell over in flight and landed on their sides which caused a lot of duds in soft ground. It fired high-explosive and gas shells. For transport two wheels from the Gebirgsgechütz M 99 were used.
The M 17 version of this weapon had an elevation screw with a double thread and reinforced trunnion bearings. It's unclear how the M 16 differed from the earlier model.