The 'Lucky 15' bet is a popular multiple bet, which involves 4 selections, amounting to 15 invdividual bets across those. This bet type consists of 4 singles, 6 doubles, 4 trebles and 1 four-fold accumulator. In order to gain a return, the bettor requires just one of the four selections to be settled as a winner.
You pick your 10 winners and then make every possible fivefold bet from them all. This is called a fivefolds from 10 selections bet but if you were unsure of a couple of games you might just pick the winner of eight of the 10 matches and opt for a fivefolds from eight selections instead.