Dependent essentially mean without replacement in this case.

The probability the first winner is from Wells would be 5/15=1/3

Now, since there is one less from Wells and one less total to draw from, the probability the next winner is from Wells would be 4/14=2/7. Assuming the first winner is from Wells.

So, \(\displaystyle \frac{1}{3}\cdot \frac{2}{7}=\frac{2}{21}\)

That is the dependence. The drawing of the second depends on the first because they are not replaced.

Now, if somehow there were replacement, then it would be independent. As in cards, for instance.

If the card were not put back in the deck, the second draw would be dependent. If it were put back, then independent.

See what I am getting at?. Taking something out and not replacing it changes the probability.