In economics, there is a formula to predict the growth of money value with time. When dealing with simple interest, the formula is
F = P(1+in), where F is the future worth, P is the present worth, i is the annual interest rate, and n is the amount of time, commonly in terms of years. Substituting to the formula,
F = $23,000(1+0.08*15)
F = $50,600