Complex sentence: Over the course of 20 years, Haarlem Model United Nations has tripled in size with 600 expected participants at the 2017 conference, which will be held from March 31st 2017 till April 2nd 2017.
Split into simpler sentences: Over the course of 20 years, Haarlem Model United Nations has tripled in size, with 600 expected participants at the 2017 conference. The next session will be held from March 31st 2017 till April 2nd 2017.