The maximum percentage of a listed company (self-interest threat)

Dear Tutor,

Below is my question.

To avoid a self-interest threat arising, auditors of a listed company should normally not receive more than a certain percentage of their total fees from that client.

What is the recommended maximum percentage of fees?

A. 15%
B. 10%
C. 5%
D. 20%

I chosen A, but the answer is B, why? In the lecture note, it explained the maximum percentage for “listed company” is 15% right? Am I right?

For your information, this is the question in the mock exam.