15、From a complete deck of cards, at least $\qquad$ cards must be drawn to ensure that at least 6 cards have the same suit.
Analysis: A complete deck of playing cards has only 54 cards, including two jokers and 13 cards of each of the four suits. According to the worst-case principle: first take the two jokers, then take 5 cards of each suit, at this point, taking any additional card will definitely result in 6 cards of the same suit. Therefore, at least $2+5 \times 4+1=23$ (cards) need to be drawn.