There should be about a 1-in-5 chance for a treaty proposal to be made if you don't have a treaty in place and about a 1-in-20 chance for changes to a treaty. But I guess with 15 players, there's the potential for a lot of chatting. I wonder though if the 1-in-5 new treaty chance is being checked even if there is a treaty in place... hmm...
That non-aggression treaty would be broken. It also means I have a small error in that script.
I included combat reports because I tried to include all elements in the AI's routine that players might want. You may consider revising your treaties not to have combat reports if it's too much info for you - which I suspect it would in a 15-player game.