15. Given the sequence $\left\{a_{n}\right\}, a_{n}+a_{n+1}=n \cdot(-1)^{\frac{n(n+1)}{2}}$, the sum of the first $n$ terms is $S_{n}$, and $m+S_{2015}=-1007, a_{1} m>0$. Then the minimum value of $\frac{1}{a_{1}}+\frac{4}{m}$ is . $\qquad$
$$
a_{2}+a_{3}=-2, a_{4}+a_{5}=4, a_{6}+a_{7}=-6, a_{8}+a_{9}=8, \cdots, a_{2014}+a_{2015}=-2014 \text {, }
$$

Thus $S_{2015}=a_{1}-1008 \Rightarrow a_{1}+m=1$. Therefore $\frac{1}{a_{1}}+\frac{4}{m} \geqslant \frac{9}{a_{1}+m}=9$, equality holds when $a_{1}=\frac{1}{3}, m=\frac{2}{3}$, so the minimum value of $\frac{1}{a_{1}}+\frac{4}{m}$ is 9.