First of all the person was talking about the flu vaccines - we weren't talking about those rare diseases. His clinical insight is probably on track, and I'm sure if you spend the time looking you'll find the same.
Completely wrong. Flu vaccines are not 15% effective. They are close to 100% effective for the strains they target. They are roughly 60% effective for a given year because there are so many strains, and the vaccine can only target 3 or 4 of them. However, even when they miss a strain, they often cause the disease to be much milder than it would be with no vaccine.