Should I negotiate my severance? - what worked for you?

I was offered 15 weeks of severance after 15 years as a recruiter, and I have a few days to sign. There are 15 people counting on me, so I am trying to be careful. It includes health coverage for a couple of months. Did anyone negotiate and succeed?

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.