On 14 November 2016, an ATR72-600 crew lost control at FL150 in severe icing conditions. Uncontrolled rolls and a 1,500 feet height loss followed during an apparent stall. After recovery, the Captain announced to the alarmed passengers that he had regained control and the flight was completed without further event. The Investigation found that the crew had been aware that they had encountered severe icing rather than the forecast moderate icing but had attempted to continue to climb which took the aircraft outside its performance limitations. The recovery from the stall was non-optimal and two key memory actions were overlooked.