The Giver is in terrible pain, and he asks Jonas to take the memory, which he is having. He gives Jonas a memory of a war, where a man injured and dying on the battlefield. In the memory, Jonas is a young man who gives another badly injured solider water and then stays with the other soldier as he dies. Jonas is himself injured, and the pain he feels is terrible. Then the Giver is apologize for that and asks Jonas to forgive him, although they both know that The Giver didn’t have the strength to carry the memory himself any longer.
This was a short summary of the chapter 15, I hope it will be helpfull for you :)