Explanation:
The perpendicular line *always* has a slope of the negative reciprocal. Your given line has a slope of -5, so the perpendicular slope is -1/(-5) = 1/5.
Use the point-slope form of a general line to find the equation.
(y - y_1) = m * (x - x_1)
y - 7 = (1/5) * (x - 15)