Complex sentence: Inaugural edition of Marathon in 2012 saw 1,500 participants, since then number of participants has been increased, recent 2015 edition saw more than 4,000 participants from 20 countries.
Split into simpler sentences: Inaugural edition of Marathon in 2012 saw 1,500 participants, since then number of participants has been increased. Recent 2015 edition saw more than 4,000 participants from 20 countries.