Supernatural's 15th and final season was meant to end on May 18, but the ongoing novel coronavirus (COVID-19) pandemic has changed the timeline a bit. Executive producer Andrew Dabb announced on Twitter that the season's 13th episode, airing on March 23, will be the last new episode to air "for a while." He went on to explain that although the series has filmed through episode 18, "our visual effects and sound departments have closed because of the outbreak. So, right now, the episodes can't be finished."
(Clarification: We have filmed through episode 18, however our visual effects and sound departments have closed because of the outbreak. So, right now, the episodes can't be finished. However, have some special treats coming along the way-- to help us all get through this.)— Andrew Dabb (@andrewdabb) March 23, 2020
All this goes to say that the production of the final season has put on the brakes, which pushes back the originally scheduled date of the series finale. At the time of the shutdown, the series was only two episodes shy of wrapping up the entire 20-episode season, but Dabb assured fans that everyone is still on board to finish the Winchesters' story. "We, The CW, and Warner Bros. fully intend to return and finish the series," he wrote on Twitter. "It's not a matter of 'if,' it's a matter of 'when.'"
As of now, there is no update on when the series finale will officially air, but we'll keep our eyes peeled for any news!