As Hudson's airplane is in Australia (where the air is different), its relevant to quote from the Civil Aviation Safety Authority Australia's "Flight Instructor's Manual". It is out of print but still referenced by the new, draft Manual of Standards.
"Recovery when the Wing Drops"
Use the standard recovery, ie, simultaneous use of power and forward movement of the control column. In addition rudder must be used to prevent the nose of the aeroplane yawing into the direction of the lowered wing. The ailerons should be held neutral until control is regained, when the wings should be levelled. In aeroplanes where the ailerons remain effective beyond the critical angle, they may be used to regain or maintain lateral level in association with the rudder."
I have rejected airplanes off a production line for unacceptable stall behaviour - back to change the rigging. I've flown in-service airplanes where pilots have complained about their handling and given my opinion that they were acceptable. I've flown in-service aeroplanes where I've wondered how it was certified with a wing-drop like that - it wasn't just one example of the type.
Hudson presumably knows how a typical Cessna behaves, has he sought advice from other pilots who have flown it?
In considering the regulatory requirement you must start with the Type Certificate Data Sheet for that particular aeroplane and go to the original certification standard. Look at the configurations required to be tested. The 15 deg limit on roll doesn not apply to all situations - some simply require that "it shall be possible to recover" - quoting from the old Civil Air Regulations Part 3 here.