If you started with $100 (on red, before the first black you mentioned) and were applying the double-your-bet-after-a-loss strategy, that 16th bet would've cost you $3.2 million, just to win that initial $100. Starting after the 4th black, the 12th bet (after the 15th black in a row) would've only cost you $204k (again, to win that initial $100).