第一句：

So before struggling to sort through the likes, dislikes, quirks and wishes of the people on your holiday lists, you may want to consider some recent findings about which gift-giving strategies work. 

第二句：

For the past 15 years or so, the received wisdom in behavioral economics has been that buying experiences, or giving them as gifts, produces more happiness over the long run than purchased material things do. 

 第三句：

So sometimes it comes down to which kind of happiness you wish to convey. 

这三句的so，第一，三为连词，第二句的so为副词，相当于about 15 years?是不是如果承接句子的意思so一般为连词，而在形容词或者副词前的一般为副词？