Trini,
Sorry to hear about MIL. However, £1500 is on the really high side. You must be beside yourself with worry. I have done research into Care Homes for mother. The ones charging this amount were the most expensive in her area - Essex - and were providing specialist dementia care. But this amount of money is ridiculous.
But first of all, what assessments have been made into your MILs finances?
You should have an assessment fo what income your MIL has and what savings she has. If she owns the property you are living in a charge may, operative word, may be raised against it. However, if it is your own property, there should be nothing that you should be paying for.
Please, as a matter of urgency, contact these organisations who will give you all the information you need and guide you.
Alzheimere's Society
https://www.alzheimers.org.uk/
I have found the above a superb source of information and a good place to offload. They may also be able to guide you, not suggest, other appropriate homes in the area. They have a good insight into how things work in your area and will help you work your way through.
Scroll down the page and put in your postcode.
Age UK
Same as above.
http://www.ageuk.org.uk/?gclid=CjwK..._6y-vPpp8STtWBdfyc-1ahoCZgXw_wcB&gclsrc=aw.ds
I have done a lot of research into to care homes in mother's area. they range from @ £1,8000 down to £600pw for the ones I was happy to get mum into. I learnt from Ann Mac's thread, So Bizarre, the big ones do not necessarily provide the care she was happy with. It has been a lot of research. I have now found 3 I am happy with and I am fussy. They start at £600 pw. Mother has a reasonable-ish pension and her savings, currently, put her over the limit. However, on speaking with the care homes when mother's savings run out - which would be fairly quickly, two things would happen. Firstly, SS then put in the Local Council weekly financial support, plus or minus £500 per week. Your local County Council will be able to tell you what they provide in care home support. Secondly, the care homes would then put mother onto the same charge rate for SS funded homes - so bring it down.
I really hope that some of this helps you.