Manganese oxides have attracted great interest in solid-state physics research owing to the diverse range of electronic ordering phenomena. Pb3Mn7O15 is a relatively understudied complex oxide that displays spin, charge and orbital ordering on a geometrically frustrated lattice. We propose a WISH experiment to investigate the magnetic structure in the two long-range ordered phases below TN=70 K. We will solve the exact spin configurations and determine the behaviour of the antiferromagnetic propagation vector and magnetic order parameter as a function of temperature, essential in unravelling the microscopic interactions between spin, charge and orbital order. Furthermore, Pb3Mn7O15 is predicted to have magneto-electric properties. Evaluating the magnetic structure at low temperature will confirm whether or not this material is a candidate for novel multiferroicity.