Severance offer, what should I ask for? - 26 weeks in

I was offered 15 weeks of severance after 15 years as a home health aide, and I have a few days to sign. There is a non-disparagement clause. Did anyone negotiate and succeed?

I asked for two more weeks and a neutral reference. They agreed to the reference and added a week.

An hour with an employment lawyer cost me a small fee and made me feel much safer about signing.