What could a 15 word phrase be used for in relation to DNMs? For example, know how some online wallet services or even apps like electrum generate a seed or brainwallet phrase that you can recover a bitcoin wallet with? Did any markets in the past, such as Evolution, Agora, or even SR2 use one during signup for wallet or even account recovery purposes? As far as I know, most brainwallet/seed phrases only use 12 words, not 15.
I know AB used one but it was really short from what I remember.