There is a big difference between 9:15 and 9:45. HH suggests 30-90 seconds slower than goal for experienced runners. 30 seconds is on the high end of things. Most people should be running closer to the 90 side (I run a 1:37 and most of my runs are in the 9 min/mi range). If you have 20-30 MPH headwinds, you should adjust your pace to match your RPE to easy. Easy is easier than never being out of breath, it is being able to have a conversation without being out of breath.

To determine if you goal is obtainable, you should have done the goal races (or at least time trials) at all out efforts as HH prescribes then use an online race predictor as stated in his plan. Without these it is hard to tell if you are overreaching your goal or just going through fatigue (possibly because you are pushing your easy efforts too much).