Complex sentence: The most successful team in the league is Oostende, which holds the record for the most league titles won, with 16, and the now defunct team of Racing Mechelen is second, with 15.
Split into simpler sentences: The most successful team currently active in the league is Oostende, which holds the record for the most league titles won, with 16. The now defunct team, Racing Mechelen, is currently the team with the second most league titles won, with 15.