The difference is in the power control logic of ROSCO. The IEA22 uses the constant power control (IEA-22-280-RWT/OpenFAST/IEA-22-280-RWT-Monopile/IEA-22-280-RWT_DISCON.IN at fe07471393c5b61eb0c7072bbfe2337ae80f3a81 · IEAWindTask37/IEA-22-280-RWT · GitHub), whereas for the IEA15 ROSCO uses the constant torque control (IEA-15-240-RWT/OpenFAST/IEA-15-240-RWT-Monopile/IEA-15-240-RWT-Monopile_DISCON.IN at 2575756896ab45575ab1c094da76fde65a3d1d47 · IEAWindTask37/IEA-15-240-RWT · GitHub). You should be able to see the difference in the torque signals