DD(3) is in the process of being dx with probable ASD. She's in mainstream nursery but we'll almost certainly need to HE her instead of sending her to primary school, at least initially. She wouldn't be able to cope with the hours, the rules, the number of other children, the uniform etc..... No schools round here will compromise on any of these (I checked).
But she loves her nursery! They are small, quiet, gentle and they really work to help her. She would be due to start reception in September 2016 but won't turn 5 until March 2017. Given no primary school will be using her 15 hours funding would nursery be able to keep her until she turns 5?
If you want to send her part time to primary school in September 2016, the school cannot refuse to let you. You simply let them know that she will be part time for the first 2 terms. She will need to go full time after Easter 2017 though.
But, to answer your question, yes, you should be able to use her 15 hours funding until she is 5. It will depend on you being able to find a nursery who is willing to take her (as an older child).
I suggest you speak to your local authority admissions team so that you can quote the rules to the school!
Also, you can choose to accept the place, and then defer her attendance until the summer term if you want. If her birthday is in March, education (or in this case, school attendance) is not statutory until the term after she is 5 (ie. the summer term). The school cannot stop you doing this either. You just need to accept the place in the usual way and then inform the school you will be deferring her place for 2 terms. It does mean that she would only do one term in Reception though, before moving into year 1.
I know I can defer, but tbh she won't be ready for school proper for a good while yet. Nursery is good as they are prepared to be almost entirely child-led in her case. If only there was a truly Montessori school near here!