A year repeats its calendar if it is a non-leap year and occurs after a gap of 6 years or 11 years from the previous identical year. The year 2009 was not a leap year. The sequence of days of the week repeats every 7 days. However, calendar years repeat when the total number of days between two years, considering leap years, is a multiple of 7. The year 2015, being 6 years after 2009, also did not have an intervening leap year (2012 was the leap year before 2015). Thus, 2015 has the same calendar as 2009.