How many orbitals contain one or more electrons in an isolated ground state iron atom (Z = 26)?

$ \textbf{(A) }13 \qquad\textbf{(B) }14 \qquad\textbf{(C) } 15\qquad\textbf{(D) } 16\qquad$
1. Determine the ground state electron configuration for an iron atom (Z = 26). The electron configuration is:
   \[
   1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2
   \]

2. Identify the orbitals that contain at least one electron:
   - The 1s orbital contains 2 electrons.
   - The 2s orbital contains 2 electrons.
   - The three 2p orbitals contain a total of 6 electrons.
   - The 3s orbital contains 2 electrons.
   - The three 3p orbitals contain a total of 6 electrons.
   - The five 3d orbitals contain a total of 6 electrons.
   - The 4s orbital contains 2 electrons.

3. Count the number of orbitals that contain at least one electron:
   - 1s: 1 orbital
   - 2s: 1 orbital
   - 2p: 3 orbitals
   - 3s: 1 orbital
   - 3p: 3 orbitals
   - 3d: 5 orbitals
   - 4s: 1 orbital

4. Sum the number of orbitals:
   \[
   1 + 1 + 3 + 1 + 3 + 5 + 1 = 15
   \]

Conclusion:
\[
\boxed{15}
\]