The average throw of a die can be computed by throwing six die, with each die representing 1 number and then dividing by six.
1 + 2 + 3 + 4 + 5 + 6 = 21
Average value per roll of a die = 21 / 6 = 3.5
Average value per 5 dice = 3.5 * 5 = 17.5 > 15.5
Take the over.