This is similar to looking into a makeup or shaving mirror when your face is very close to it—you see an upright, magnified reflection of yourself that appears to be deep inside the glass.

When the object is closer than the focal point, the image goes behind (Virtual, Erect, Magnified).

According to the mirror formula, the relationship between focal length $f$, object distance $u$, and image distance $v$ is given by $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$. Substituting $f = -15\text{ cm}$ and $u = -10\text{ cm}$ following the New Cartesian Sign Convention, we solve for $v$ to get $+30\text{ cm}$. The positive sign of $v$ confirms that the image is formed behind the mirror.

Always double-check signs when applying the mirror formula; object and focal lengths for concave mirrors are negative in real-object scenarios.