The conference was in June 2015. The paper would have been submitted for peer review in Summer/Fall 2014. Which means that it could have been written in Winter/

The conference was in June 2015. The paper would have been submitted for peer review in Summer/Fall 2014. Which means that it could have been written in Winter/Spring 2014. SIGMOD is not like a dev conference where you can change the paper the day before your talk.