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