The slope of L1 would be (15-5)/(2+3) = 2 and the slope of L2 would be (1-2)/(-7+4) = 1/3. For a line to parallel, the two slopes would have to be the same and for a line to be perpendicular, the slopes would have to be the negative reciprocal of eachother therefore the lines are neither parallel nor perpendicular.
