Square Enix has been shuffling composition duties for the Final Fantasy series among a number of composers in recent years, and former Square Enix composer Yoko Shimomura will be continuing that tradition. She was originally tapped to score Final Fantasy XV when it was still known as Final Fantasy Versus XIII, so it makes sense that she's continued on with the project after its rebranding.
According to a source close to development, Shimomura will be scoring Final Fantasy XV alone, and an orchestrator is yet to be determined. This will mark her first foray into the Final Fantasy series, with past composers including Nobuo Uematsu (XIV), Masashi Hamauzu (XIII), and Hitoshi Sakimoto (XII). While she's best known for her work on the Kingdom Hearts series (including the upcoming Kingdom Hearts III), she's also worked on Legend of Mana, Parasite Eve, and Front Mission.
I'm certainly looking forward to hearing more.