\[y = \frac{x^{2} - 2x - 15}{x + 3} =\]
\[= \frac{(x + 3)(x - 5)}{x + 3} =\]
\[= x - 5;\ \ x \neq - 3.\]
\[x^{2} - 2x - 15 = (x + 3)(x - 5);\]
\[D_{1} = 1 + 15 = 16\]
\[x_{1} = 1 + 4 = 5;\ \]
\[x_{2} = 1 - 4 = - 3.\]