You challenge the 15,000 number based on ... your worldwide examination of actual diagnosis of HoFH patients? No wait, that is where the 15,000 number came from. If you don't believe in that number, then you must be using the theoretical projection from the probability model instead.
What will you do when they find the mathematical error in the probability model? Arthur, you simply don't get it do you? The 15K number is based on REALITY. How many people ACTUALLY HAVE HoFH. Real patients diagnosed. Not some outdated guess.
This is the same situation as breast cancer and many other diseases that were thought to have much lower incident rates before they had treatments. Then, when treatments were developed, the true patient count skyrocketed.