根据英语惯用法,在 “It is/has been + 段时间+ since 从句”这种句型中,since 从句通常用一般过去时,It后面通常用 is (一般现在时)或者has been (现在完成时): is 是英国英语用法,has been 是美国英语用法。如:
(US) It has been over ten years since I last visited Europe. = (Brit) It is over ten years since I last visited Europe. 距我上次访问欧洲已经有十多年了。(《韦氏高阶英汉双解词典》p.1948)