loan modification only 15% principle reduction

Can someone confirm the following:
someone told me that there is a law out there that states that loan modifications can only be reduced 15% of the principle. I’m in California.

I can’t attest to any law limiting principal reduction to 15%. If you are negotiating a loan modification with a lender the lender can do anything they want. They can write off 75% of the loan amount if they feel like taking the loss.