it is 15% of your 50% entitlement - which makes it 7.5% of the total bill

for example, bill is $100, your CCR is 50% (so $50) - 15% of your $50 is withheld (so $7.5) - which is the same as 7.5% of the total bill

ETA - this means 42.5% of the bill is paid to the child care as your CCR (50% less the 7.5%)