Severance offer, what should I ask for? - 3 months and counting

I was offered 15 weeks of severance after 15 years as a recruiter, and I have a few days to sign. I do not want to leave money on the table. Should I see a lawyer?

Thanks for writing this out. I went through something close to it 3 months ago, and it got easier once I kept a simple log of every call and form.