15. The parametric equation of line $l$ is $\left\{ \begin{array} { c } x = - 1 + t \\ y = 1 + t \end{array} \right.$ (where $t$ is the parameter). With the origin as the pole and the positive $x$-axis as the polar axis, the polar equation of curve $C$ is $\rho ^ { 2 } \cos 2 \theta = 4 \left( \rho > 0 , \frac { 3 \pi } { 4 } < \theta < \frac { 5 \pi } { 4 } \right)$. The polar coordinates of the intersection point of line $l$ and curve $C$ are $\_\_\_\_$ .\\