Of course, the 150 WAS designed for it. And spin vs. no spin training has always been a big debate. I've always found it interesting how easy it is to spin a 150, especially with power applied. I did my flight training in Canada where spin training is still mandatory, and the 1974 vintage 150 training aircraft I flew probably had more spins in its history than I could ever count. My instructor liked doing spin entry with power, since that would likely be the scenario in an approach gone wrong. The stall horn rarely got a chance to go off and there was very little buffet before the aircraft would roll over into a very well developed spin (very pretty over the fall colors of the Ottawa Valley). Also, it's no wonder you didn't get horn. If memory serves, the stall horn is on the left leading edge, and you were likely making a turn to the right. so your right wing would have stalled first. Worst "almost incident" we had was when a student did the preflight and filled the tanks prior to his lesson. The student was 230lbs + and the instructor was at least 200 (putting the little 150 over gross.) The instructor had been flying spins all day (the class was all at that point in the training) and so the instructor was a bit tired to notice the over gross situation. The instructor entered a demonstration spin and the aircraft would not recover using the standard method. Faced with no other choice the instructor threw in power - knowing the results could go either way. We suspect a combination of the yaw input from the prop and the increased airflow over the tail allowed them to recover from the spin. Stupid thing to get in to. Good thing he was familiar enough with spins to know his options.