The tattoo 15 may have significant meaning for the person who has it. It could represent a birthdate, a lucky number, or a tribute to a loved one who passed away at the age of 15. It could also represent a milestone in their life such as a graduation, an achievement or a special memory. For some people, 15 may be a reminder of a life-changing event or experience. Ultimately, the meaning behind this tattoo is specific to the individual who has it and its significance to them.