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

I was offered 16 weeks of severance after 16 years as an accountant, and I have a few days to sign. I do not usually post, so bear with me. I do not want to leave money on the table. Did anyone negotiate and succeed?

Thanks for writing this out. I went through something close to it 14 months ago, and it settled down once I kept a simple log of every call and form.