CAIRO — The Egyptian authorities hanged 15 men on Tuesday for an attack in the Sinai Peninsula in 2013, the start of an Islamic insurgency that the military-dominated government has been battling ever since. The hangings, reported by state media, were the biggest mass execution in Egypt since six convicted jihadists were hanged in 2015. A military court found the men guilty on terrorism charges last month for an attack on a military checkpoint in which one army officer and eight soldiers were killed. That assault came amid a surge of violence that swept across Egypt after Egyptian security forces...