Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for the n=4 and 5 complexes in Fe XV. We include in the calculations all the configurations in the n=3, 4, and 5 complexes, corresponding to 283 fine-structure levels. We also provide accurate A values for the n=3 complex. Collision strengths are calculated at five incident energies for all transitions: 12.1, 28.2, 50.4, 80.9 and 123.0 Ry above the threshold of each transition. An additional energy has been added, whose value is between 0.00075 and 0.40 Ry, depending on the transition. Calculations have been carried out using the Flexible Atomic Code and the distorted-wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. We combined the excitation rate coefficients and the radiative transition rates calculated in the present work with R-Matrix results available in the literature for the n=3 complex, to solve the statistical equilibrium equations for level populations at electron densities in the 10 8-10 14 cm -3 range and at an electron temperature of logTe(K)=6.3, corresponding to the maximum abundance of Fe XV. Spectral line intensities are calculated and compared with available observations.