No, that is not what curious meant. 20/15 is better than 20/20. I have normally without glasses about 20/150 vision, but with glasses 20/15. The numbers refer to what can be seen sharply at twenty feet, and compares it to an apparent distance. To a normal person, what looks clear at 150 feet is what would look clear to me at 20 feet. 20/150. With glasses, what looks clear at fifteen feet to a person with 20/20 vision, looks the same to me at twenty feet. That is the point of their question.
I don't know what the answer to their question is, but I am watching to see if someone else does.