If you want a serious answer, here goes. The singles will stand and any multiple bets with the clashing horses will be settled with stakes divided. So for £1 stake, you would have the double on the two settled as 50p on each, the two trebles with both horses settled as 50p doubles, and the accumulator settled as three 50p trebles. Only 11 bets of the 15 would require split stakes.
If you want a serious answer, here goes. The singles will stand and any multiple bets with the clashing horses will be settled with stakes divided. So for £1 stake, you would have the double on the two settled as 50p on each, the two trebles with bo