Should I negotiate my severance? (update)

I was offered 16 weeks of severance after 16 years as a paralegal, and I have a few days to sign. I do not usually post, so bear with me. There is a non-disparagement clause. Should I see a lawyer?

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

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