By Orbit-Stabilizer Theorem and Burnside's lemma, the number of distinct orbits is the average number of points left fixed by an element of $G$.$$|X/G|={\frac {1}{|G|}}\sum _{g\in G}|X^{g}|=\frac{1}{24}\left(1\times n^{14}+8\times n^2+6\times n^2+3\times n^2+6\times n^0\right) = \frac{n^{14}+17n^2+6}{24}$$