The atomic number of an element represents the number of protons it has. For an element with an atomic number of 6, it has 6 protons.
The atomic mass (or atomic weight) is approximately the sum of the number of protons and neutrons in the nucleus of an atom. In this case, the atomic mass is given as 15.
To find the number of neutrons, you can use the following formula:
\[ \text{Neutrons} = \text{Atomic Mass} - \text{Atomic Number} \]
Substituting the values:
\[ \text{Neutrons} = 15 - 6 = 9 \]
So, the element has 9 neutrons.