The 115 car has a completely different heater core. The valves for a 111 are 000 835 03 20 - right, and 000 835 04 20 - left. The valve on the 115 is shown as an assembly controlling both sides. The actual valves inside could possibly be the same since they have the same part number for the seal (o-ring). The seal for both cars is 000 835 58 98 and is readily available from MB dealers for a few dollars. Here's a link to the Ponton group site with a good R&R explanation for the valves: Mercedes-Benz Ponton Heater Core Valve Repair © www.mbzponton.org
Even though the heater cores are different in the Ponton the method of repair is the same. With a 111 it can be done with the valves bodies in the car.