15. Today, arrange $n(n \geqslant 2)$ women and $m$ men to sit around a round table $(n+m$ seats are numbered), such that there are at least $k(m \geqslant n k)$ men between any two women. Find the number of different seating arrangements.
15. $m!(n-1)!(m+n) \cdot\binom{n+m-n k-1}{n-1}$.