TC11 is for storing recruits. It’s extra cheap slow training, takes 2 recruits and 2 hours to complete, minimal amounts of food.
You can store days of training there, and pull it out as you need to use on your other training camps.
This is good because it means you don’t need super upgraded houses to store many recruits, you can just use the Training Camp at level 11 to store an infinite amount via this training.
Level 12 gets you guaranteed 3* heroes. Level 13 gets you 3* heroes with a small chance at 4* heroes. Personally I think 12 is worth doing if you’re lacking in 3*s. Otherwise I’d skip researching it and focus on getting to level 13. However you also need a minimum cap of 70 recruits for this level.
I would recommend to get to province 15 as soon as you are able to Atlantis Rises happens every 4th Thursday of each month though, so don’t force it if your heroes still need more training.