The specifications seem to say that it requires 11.8A at 120V, and also 13.6A at 240V. So you need two dedicated circuits for this thing. The NEC would allow the 120V circuit to be a 15A, and the 240V to be 20A. I can't tell for sure from the diagram, but chances are you'll need to install these receptacles inside the wall (mounted sideways on a stud), and have an access panel on the other side, since this shower does not appear to be a removable appliance.