Read the same interval from a parabola and a sign line

$y=x^2+2x-15=(x+5)(x-3)$. The roots are x=−5 and x=3. Negative polynomial values mean the graph lies below the x-axis, which occurs for −5<x<3.

Factor $(x+5)(x-3)<0$. Mark its zeros −5,3 and test convenient inputs in $(-\infty,-5)$, $(−5,3)$ and $(3,\infty)$; for example −6,0,4 give positive, negative, positive values. Hence −5<x<3. The source test-point paragraph accidentally writes $(x-5)(x+3)$; test the original $(x+5)(x-3)$ instead, consistent with its roots and final answer.