The Ohio teen allegedly caught with an AK-47 in a Times Square subway may have just been confused about New York’s gun laws, his lawyer tried to argue in court on Sunday. But Manhattan judge Melissa C. Jackson rejected that argument — and the prosecutors’ request that bail be set at $25,000 — as she ordered that 18-year-old Saadiq Teague stay behind bars until his next court date. “This is an extremely serious case. The case is up to 15 years in prison,” Jackson said. It was the teen’s first appearance in court since he was busted around 12:30 p.m. Friday on the mezzanine level of the A, C and E station, allegedly with the weapon out next to him in plain sight. The AK-47 was unloaded, but Teague had a fully loaded magazine in his backpack, along with a gas mask, sources previously told The Post. According to a high-ranking police source, Teague told cops he thought that carrying an unloaded rifle with the ammunition stored separately is legal in New York City. His lawyer, Jacqueline Phipps, also said it was possible that her client was naïve about the Big Apple’s gun laws.