Border Patrol agents nabbed 15 illegal immigrants listed on the FBI’s terror watch list trying to sneak across the US-Mexico border in May — a month that also saw a record number of migrant encounters, according to official figures. The possible terrorists were among the staggering 239,416 migrants encountered at the southern border last month, according to a breakdown of Customs and Border Patrol figures first reported by the Washington Times and obtained by The Post. The total number of May crossings marks the highest number of migrant encounters recorded in one month ever and brings the total migrant encounters in FY 2022 to more than 1.5 million, according to the latest data released by CBP Wednesday. Experts warn that the rising number of illegal immigrants attempting to cross into the US could mean that many others on the terror list may be sneaking in undetected. “The big worry is with the chaos down there, when you have these kinds of people coming to the border, you have to assume that some of them got in,” Todd Bensman, author of “America’s Covert Border War,” about how terrorists try to exploit the immigration system, told the Washington Times.