我先把句子还原你会好理解点：
these TV shows are designed to appeal mainly to viewers who are aged between 15 to 25,该句子把who are 省略掉了使句子更精炼.其他含which is这类句子也能用同样方法,如：
TV shows which are designed for viewers above 18 cannot be publicly broadcasted...可以省略为 TV shows designed for viewers above 18 cannot be publicly broadcasted.
来自分类排名第一的英语牛人团,是信心的保证,