Barry wrote 6 different numbers, one on each side of 3 cards, and laid the cards on a table, as shown. The sums of the two numbers on each of the three cards are equal. The three numbers on the hidden sides are prime numbers. What is the average of the hidden prime numbers?

[asy]path card=((0,0)--(0,3)--(2,3)--(2,0)--cycle);

draw(card, linewidth(1));
draw(shift(2.5,0)*card, linewidth(1));
draw(shift(5,0)*card, linewidth(1));

label("$44$", (1,1.5));
label("$59$", shift(2.5,0)*(1,1.5));
label("$38$", shift(5,0)*(1,1.5));[/asy]

$ \textbf{(A)}\ 13 \qquad 
\textbf{(B)}\ 14 \qquad 
\textbf{(C)}\ 15 \qquad 
\textbf{(D)}\ 16 \qquad 
\textbf{(E)}\ 17$
1. Let the numbers on the hidden sides of the cards be \( x \), \( y \), and \( z \). The given numbers on the visible sides are 44, 59, and 38.
2. Since the sums of the numbers on each card are equal, we can write the following equations:
   \[
   44 + x = 59 + y = 38 + z = S
   \]
   where \( S \) is the common sum.
3. We know that \( x \), \( y \), and \( z \) are prime numbers. Since 59 is an odd number, the sum \( S \) must be odd (because the sum of an odd number and an even number is odd). Therefore, \( y \) must be 2, the only even prime number.
4. Substituting \( y = 2 \) into the equation \( 59 + y = S \):
   \[
   59 + 2 = S \implies S = 61
   \]
5. Now, we substitute \( S = 61 \) into the other equations to find \( x \) and \( z \):
   \[
   44 + x = 61 \implies x = 61 - 44 = 17
   \]
   \[
   38 + z = 61 \implies z = 61 - 38 = 23
   \]
6. The hidden prime numbers are 17, 2, and 23. To find the average of these numbers, we calculate:
   \[
   \text{Average} = \frac{17 + 2 + 23}{3} = \frac{42}{3} = 14
   \]

The final answer is \(\boxed{14}\).