The 15th season of the Top Chess Engine Championship began on the 6 March 2019 and ended on 12 May 2019.

The season featured for the first time two separate Division 4s, the winners of which moved to a playoff for promotion to Division 3. Also notable is the emergence of a new neural network-based engine based on AlphaZero, AllieStein, which reached the premier division, and Leela Chess Zero's victory in the superfinal, which marks the first time a neural-network engine has won the superfinal.

The season was structured into six divisions: two Division 4s (4a and 4b), Division 3, Division 2, Division 1, and the Premier Division. In Division 4, the top two engines advanced to a playoff against each other, with the top two finishers moving up to Division 3. The structure from Division 3 onward remained consistent with previous seasons: the top two engines in each division advanced to the next higher division, while the bottom two engines were relegated. The top two engines in the Premier Division competed in a 100-game superfinal. The length of the opening books used increased as the divisions progressed, and the time control ranged from 30 minutes + 5 seconds per move in Division 4 to 90 minutes + 5 seconds per move in the Premier Division.

After the controversial game 66 in the previous season's superfinal, TCEC modified its rules for disconnects: in most situations, instead of a restart from scratch, the games will be resumed from the last available position, albeit with time compensation for both engines to fill up their hash tables. The only other significant change is to remove the number of Black wins from the tiebreak criteria, leaving the tiebreakers as 1) number of crashes; 2) direct encounter; 3) number of wins; 4) Sonneborn–Berger score; 5) tournament director decision. Beyond that, the season used the standard rules of the TCEC.

Nemorino, which had been relegated in Season 14, convincingly won Division 4a. It scored 13 wins in 18 games, and conceded only one loss, to finish 2.5 points ahead of the next-nearest competitor. Second place was more hotly contested. RubiChess defeated Winter head-to-head twice, but also lost both games to Nemorino. Winter scored more wins overall, but ultimately the head-to-head tiebreak meant RubiChess qualified for the playoffs.

In contrast to Nemorino's dominating performance in the other division, Pirarucu won Division 4b by only half a point, just ahead of AllieStein, who was in turn only half a point ahead of Wasp. Pirarucu lost the head-to-head against AllieStein, but also managed to dominate the lower half of the field harder than AllieStein. ScorpioNN, which had been thoroughly outclassed in the previous season's Division 4, showed it had improved tremendously to score five wins; however it was still unstable and crashed three times, leading to a disqualification.

Nemorino, RubiChess, Pirarucu and Alliestein qualified for the playoffs. In a dominating performance that showed how fast it was improving, AllieStein crushed the field and finished 3.5 points above second-placed Nemorino, winning all four of the head-to-head games against Nemorino and losing only one game to RubiChess. Despite the losses to AllieStein, Nemorino finished 1.5 points ahead of third-placed Pirarucu on the back of two head-to-head wins.

Division 3 was closely contested, with every engine winning and losing games. rofChade and Alliestein finished first and second with 18/28 and 16.5/28 respectively, ahead of third-placed Arasan with 15.5/28. Arasan had missed out on promotion in Season 14 because eventual Premier Division engines Komodo MCTS and Leela Chess Zero were also in the division, and finished third again this season. Newly promoted Nemorino found itself outmatched and finished last with 11/28.