This is a space of vector valued Siegel modular forms with real representation $\mathrm{Det}^{ 14}\otimes\mathrm{Sym}^{ 14 }$. The following table gives the dimensions of various subspaces of $M_{14, 14}(\mathrm{Sp}(4, \mathbb{Z}))$.

Total12
Non cusp2
Cusp10