In his debut North American season in 2015–16, Plachta was assigned to Arizona's AHL affiliate, the Springfield Falcons. In 46 games with the Falcons, Plachta compiled 2 goals and 7 points before he was traded by the Coyotes on trade deadline day along with a conditional 7th round draft pick in 2017 to the Pittsburgh Penguins in exchange for Sergei Plotnikov on 29 February 2016. Plachta played a total of 30 contests for Pittsburgh's AHL affiliate Wilkes-Barre Scranton Penguins during the season.