Discounted (present value) calculation
The calculation that you gave doesn't make sense. To answer this question, you should revise your definition of "present value." The definition you gave isn't specific enough to be operational:


  To me, it seems the present value cost would be the cost of what I would pay if I was accounting for the interest of the tuition.


What does present value mean? Think about it like this. How much money do you need today to pay the future costs. Well you need $\$15,000$ to to pay for the first year and $\$ X$ to pay for the second year. Why did I write $X$? Because we want to know how much money we need today to pay for the second year and that amount is less than $\$15,000$. This is because we can invest $X$ amount of dollars at $8\%$ interest so that we have $\$15,000$ in a year. So, we want to
solve
$$
X * 1.08 = 15000.
$$
Thus, the proper present value calculation is
$$
28,889 \approx 15,000 + \frac{15,000}{1.08}.
$$