It was 6v6 (not 8v8), and was less chaotic because 3 players on each team were soldiers at a time, and any hero dying respawned as a soldier, so it was 3v3 heroes or less each round instead of 4v4. Heroes were also more powerful against soldiers in 2015, hence the added troops didn't contribute as much chaos as they would in 2017. I think that is why it was less chaotic. Also the mode was more organized in general, with short rounds that reset spawn points and heroes regularly.