The funding is ot available all year round. It's 38 weeks of the year. So instead of paying the reduced cost for 38 weeks and full cost for the remaining 14, they spread it out. So your 15 hours becomes somewhere around 11 hours per week. And then you have to pay for any hours over 11
Funding is only for school term times unless you stretch it which means it's obviously less per week (about 11 hours). Some nurseries have restrictions on how many hours can be funded per day, too. I mean, your bill is pretty normal to be fair. We were paying £1400 a month per child for four days with the funding. Childcare is expensive and definitely something to do the sums on before having kids!
So they have added a consumables charge in. They actually aren't allowed to enforce that charge as it is a voluntary charge. But they are allowed to state that funded hours are only available between 9am-12pm for example. It's really not clear how many hours they are charging you for, but yes, the £600 is what you would be charged. You will be getting charged for 11 hours per day there by the looks of it so with stretched funding, you will be paying for a min on 11 hours a week. Childminders are usually cheaper so that's something you could look at