If you default on $15K I would say it's a fair bet to make that they would come after you, as in formal collection proceedings, simply due to the fact that "they want to continue being paid".

You may wanna do something sensible like discontinue using the cards you have and subscribe to a credit counselling service. $15K on one card and whatever balances on three others may be indicative of a bit of overextension, from which you may need some assistance getting out from under.