The high-resolution rotational spectrum of H15NO3 has been recorded in the range between 74 and 850 GHz and used to complete an extensive analysis of the six vibrational states below 1000 cm−1 that include the isolated 81 and 91 states along with the weakly interacting 61 and 71 states and strongly interacting 51 and 92dyad. The 61 and 71 states couple via a weak Coriolis interaction while the 51 and 91 states couple through strong Fermi and weaker Coriolis interactions. The Hamiltonian models account for the observed torsional splitting in the 91 and 92 states of 2.4 and 70 MHz, respectively, and the induced torsional spitting of 15 MHz in the 51 state due to the strong Fermi mixing with the 92 state. The transitions from each state are fit to within the experimental accuracy and the resulting spectroscopic constants agree well with the main isotopologue.