According to Wikipedia,

The MG 08/15 was a lightened and thus more portable version — by "stepping-down" the upper rear and lower forward corners of the original MG 08's rectangular-outline receiver and breech assembly, and reducing the cooling jacket's diameter to 92.5 millimeters — was tested as a prototype in 1915 by a team of weapon designers under the direction of an Oberst Friedrich von Merkatz—the MG 08/15. The MG 08/15 had been designed to be manned by four trained infantrymen spread on the ground around the gun and in the prone position. To accomplish that purpose the MG 08/15 featured a short bipod rather than a heavy four legged sled mount, plus a wooden gunstock and a pistol grip. At 18 kg, the MG 08/15 was lighter and less cumbersome than the standard MG 08 since the MG 08/15 had been designed to provide increased mobility of infantry automatic fire. It nevertheless remained a bulky water-cooled weapon which was quite demanding on the quality and training of its crews. Accurate fire was difficult to achieve and usually in short bursts only. It was first introduced in battle during the French "Chemin des Dames" offensive in April 1917 where it contributed to the very high casualty count among the French assailants. Its deployment in increasingly large numbers with all front line infantry regiments continued in 1917 and during the German offensives of the spring and summer of 1918. The MG 08/15 became, by far, the most common German machine gun deployed in World War I (Dolf Goldsmith, 1989) since it reached a full allocation of six guns per company or 72 guns per regiment in 1918. By that time, there were four times as many MG 08/15 light machine guns than heavy MG 08 machine guns in each infantry regiment. To attain this goal, about 130,000 MG 08/15 had to be manufactured during World War I, most of them by the Spandau and Erfurt government arsenals.