Any advice for help for 15 month old with autism

I would start with my GP and as what support is available to make a diagnosis and find what support there is.

Looking at what you have discussed gives a hint at autism but how about the other signs? Looking at a list from https://www.cdc.gov/autism/signs-symptoms/index.html :

Avoids or does not keep eye contact
Does not respond to name by 9 months of age
Does not show facial expressions such as happy, sad, angry, and surprised by 9 months of age
Does not play simple interactive games like pat-a-cake by 12 months of age
Uses few or no gestures by 12 months of age (for example, does not wave goodbye)
Does not share interests with others by 15 months of age (for example, shows you an object that they like)

Making notes against these points before your appointment should help the doctor take it seriously.

Please let us know what you find as I don't recall seeing many cases pcked up this young.

Yes all to all of those things, he doesn’t respond to his name, or any calling, any words at all or noises, he doesn’t gesture at all, doesn’t share anything with us, makes no eye contact, is totally indifferent to the presence of people, nurse said she could tell but just a few minutes with him but he won’t get a diagnosis for years because they refer at 2 years old then your on a waiting list. It’s too long to go without knowing how to help him. It was incredibly hard seeing his regress. It was like watching him fade away. Our baby boy is lost inside. He used to laugh and giggle at us and wave goodbye and enjoy songs. Seems so long ago now. I’ve come to terms with it but I just desperately want to know how to help him 

My advice would be to go private - get a specialist in this field, get their opinion and get them to refer it to your doctor with advice on a treatment plan. You should let them know exactly what you want as an outcome for their actions post diagnosis.

Be prepared for the situation that there is a different diagnosis though, it is very difficult to guess without the proper training with kids this young. Just try to keep an open mind until you hear but ask in writing beforehand for them to give a recommendation plan to your GP.

It will be kind of hard for the doctor to refuse in the face of this specialist opinion.

I suspect you will have to do a great deal of the work therapy wise but with the right guidance it will hopefully give results.

Of course I am just some rando on the internet so don't just take my advice - do your own research and reach your own decisions as the specialist probably won't be cheap.

My advice would be to go private - get a specialist in this field, get their opinion and get them to refer it to your doctor with advice on a treatment plan. You should let them know exactly what you want as an outcome for their actions post diagnosis.

Be prepared for the situation that there is a different diagnosis though, it is very difficult to guess without the proper training with kids this young. Just try to keep an open mind until you hear but ask in writing beforehand for them to give a recommendation plan to your GP.

It will be kind of hard for the doctor to refuse in the face of this specialist opinion.

I suspect you will have to do a great deal of the work therapy wise but with the right guidance it will hopefully give results.

Of course I am just some rando on the internet so don't just take my advice - do your own research and reach your own decisions as the specialist probably won't be cheap.