A report about the importance of this festival in Laos is on: http://mypublicholiday.com/pha-that-luang-festival.html
Phra That Luang is a holy shrine and spiritual worshiping place of the Lao people. It is a symbol of the culture and art, and inspired by the 15th century Kingdom of LaneXang. It is the biggest Buddhist holiday in Laos.
See also: https://www.torontomulticulturalcalendar.com/2013/10/26/425-laotian-festivals-in-november/
Before you venture out to any event, always check by phone for time and other changes.