One way to graph this equation is to find the x- and y-intercepts, and draw a line through those. These are easily found by putting the equation in "intercept form."

x/(x-intercept) + y/(y-intercept) = 1

x + 5y = 15

x/15 + 5y/15 = 1

x/15 + y/3 = 1

Plot the points (15, 0) and (0, 3), and draw a line through them. That is your graph.