American whites went up 1 point since 2012′s PISA, while American Asians were down 31 points (roughly 3 tenths of a standard deviation). I don’t know why. In general, East Asian countries were down a little from 2012.
There were a number of big changes in the PISA from 2012 to 2015. I think they switched from paper to computer and made some other changes as well. So it’s probably best not to worry too much about score changes from 2012 to 2015.
You can read my earlier coverage of PISA results over the years here.