Either you misread my post, or your definition of "safe" is somewhat different from mine. Assuming that the requirements were the same when the 150 was designed as they are now and it therefore complies, it can barely do so and only when in good condition. It certainly isn't easy to achieve any climb at all in a typical, battered, abused airframe with 40° flap. It is therefore not a good idea to suggest it is safe in a forum frequented by pilots of a variety of experience levels.
An instructor who has run the flying school which owns the aircraft for several years is probably about as good at flying a 150 as anyone. If he can't fly away in an area with no especially steep terrain, I reckon it isn't a safe manoeuvre!