Using a pairwise potential approximation and a shell model, computer simulation is performed of a charge-ordered crystal phase of La1.5Sr0.5NiO4, in which Ni2+ and Ni3+ ions are arranged in staggered rows in perovskite layers. This phase is found to be stable, and, in the process of its formation, the contribution to the lowering of the total crystal energy from the charge rearrangement is smaller than that from the relaxation of the crystal structure (the structure of NiO2 layers, first of all) caused by this rearrangement. The decrease in the total energy is due to the long-range Coulomb interaction, predominantly the attraction between Ni3+ and oxygen ions in NiO2 layers.