DS couldn't sit through story time / carpet time until he was 4 or 5 and even then only after we had won 35 hours a week 1:1 ABA therapy at tribunal and he had been taught how to! There will be children who are much older who still can't do it. Even now DS (age 8, mainstream year 3) opts out of very wordy carpet time and has written instructions and starts his work instead.
There are 2 issues. 1 is your entitlement to childcare - you shouldn't be discriminated against because your child is disabled / has SEN. Disability law now protects carers of disabled children.
The 2nd is your child's right to intervention to meet his SEN. This shouldn't be set by how much free childcare the govt offers (although it often is because mainstream nursery places are a cheap way for LAs to discharge their sen duties). He should receive the number of hours necessary to minimise the impact of his disability and help him achieve the best outcomes / narrow the gap with peers etc. The number of hours of education should be based on his needs. Mostly children with SEN need more education not less than other children as they have more to learn and learn slower.
This is why most special school nurseries offer more than 15 hours per week.
In our case we proved at tribunal at age 3 that he needed 35 hours per week of specialist intervention to meet his SEN. The 15 hours a week childcare offer was irrelevant, SEN law doesn't mention this at all.
To ascertain how many hours of education or intervention your child needs will require assessment by the LA either inside or outside the EHCP process e.g. a SLT / EP / Early Year Specialist teacher should assess and advise whats required.
Check out your councils website there should be a local offer and it should state what the council funds for SEN at early years / what services are available
For e.g. my LA offers 75% of 15 hours 1:1 with just written evidence from the nursery and a professional e.g. SLT. For 100% 1:1 or > 15 hours per week you need apply for EHCP.
I would consider applying yourself for EHCP but I would also self refer to the Ed Psych / Early Years specialist service and ask them to visit.
Look up SEN Code of Practice etc on Dept of Education website and read up on your rights.
You must contact the Council though be it EP or SEN team as the legal duty to educate your child lies with the Council but you can't hold them to account if they don't know theres a problem.