I suspect the "815" designates a company. In the order of battle for each infantry division I have investigated there is a classification called "special troops". The quartermaster unit is one of those and is always of company size. To the best of my knowledge platoons always had letter designations. Other than divisional quartermaster units there seems to have existed a wide variety of independent special units for such things as trucking, bath and clothing exchange, railhead, or just "service" companies that did stuff like cleaning up battle damage.