Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ar XV. The configurations used are 2s, 2s2p, 2p, 2l3l, 2l4land2s5l, with l=s,pandl=s,p,d giving rise to 92 fine-structure levels in intermediate coupling. Collision strengths are calculated at eight incident energies (10, 20, 30, 60, 120, 180, 240, and 300 Ry) for transitions within the three lowest configurations, and five incident energies (60, 120, 180, 240, and 300 Ry) for transitions between the lowest five levels and the n = 3, 4, 5 configurations, using the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, and R-matrix results for the 2s 2, 2s2p, 2p 2 configurations available in the literature, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10 8-10 14 cm -3 at an electron temperature of logT(K)=6.6, corresponding to the maximum abundance of Ar XV. Spectral line intensities are calculated, and their diagnostic relevance is discussed. Observed line ratios indicate electron temperatures of the relevant emitting plasma close to logT(K)=6.6. This dataset will be made available in the next version of the CHIANTI database.