The term 5/15 has a correlation much like that of 4/20. 4/20 is a term originated from a group of teenagers at San Rafael High School in San Rafael, California, United States in 1971.The teens would meet after school at 4:20 p.m. to smoke marijuana at the Louis Pasteur statue and the day is nationally known as national pot smokers day. A small town called Tell City High School, in Indiana began this tradition a few years back. There was nothing to do in the small suburban town so when the athletic practice would get out (at 5:00) or if there was a football game or basketball game that started at 5:30 all the jocks and the cool kids would go to the parking lot at 5:15 to drink alcohol. The same group of kids and other followers of this counter cultural type practice that arent interested in smoking weed on 4/20 now get together on 5/15 (May 15) and get plastered.
Steve: Hey man you ready for 5/15, its coming up in a few days?
John: Am I ready? I have two half gallons of captain morgan, imma be folded like a lawn chair.