15.56 is the average number of candidates per seat in the 349 constituencies going to the polls till April 24. In the previous national elections, in 2009, that number was 14.86, as 8,070 candidates competed for 543 seats, either as representatives of 363 political parties or as independents.
Source: How India Lives, a company founded by journalists, which seeks to increase the access and search of public data in India. More statistics on the largest election in history here.