Rocket League off-seasons are short so players don't have to wait too long before jumping into the next Competitive Season.
All but two of Rocket League's 14 Competitive Seasons have started on the same day that their predecessor ended. The off-season typically only lasts two hours as the servers are down for the game's update. Season 15 is still without an official launch date, but it is likely to come at the same time that the game transitions to free to play.
Rocket League Off Season: Everything You Need to Know
Rocket League Season 15 is still without a firm start date, as Psyonix had to extend Season 14 because of a major update coming later this summer. It is presumed that this major update will include the launch of free to play, which Psyonix recently announced.
Rocket League players who have played the game prior to the launch of free to play will be granted Legacy status which comes with a few bonuses. It is safe to assume that this update will also mark the end of Season 14 and the start of Season 15. If the off-season sounds too long, use the time to brush up on your skills so you can make Grand Champion in Season 15.