Do I understand correctly that you only won $1.5k from their bookie but they still confiscated $15k? If so, that's thieft 
I tried to find when they changed the TOS with no luck but my Russian friend successfully verified his account no more than a week ago and withdrew all his winnings, so it must be a very recent change. He also told me that Sportsbook is no longer available to him, so it's not really clear how you violate their TOS if they just disabled Sportsbook for any Russian player right after the TOS change.
Personally, I had a similar case when the casino put my country on the list of banned countries and retroactively canceled my winnings, but after complaining to the licensor, they obliged to pay out every penny.
I tried to find when they changed the TOS with no luck but my Russian friend successfully verified his account no more than a week ago and withdrew all his winnings, so it must be a very recent change. He also told me that Sportsbook is no longer available to him, so it's not really clear how you violate their TOS if they just disabled Sportsbook for any Russian player right after the TOS change.
Personally, I had a similar case when the casino put my country on the list of banned countries and retroactively canceled my winnings, but after complaining to the licensor, they obliged to pay out every penny.