A 4% withdrawal rate is accepted as safe, but given that I think we're likely facing a period of inflation and economic uncertainty, and 45 is a younger, riskier age to retire, I'd set that at 3%. Three percent of 15M is $450,000.

I live in SF. I'd consider $450,000 to be a comfortable figure to live on in the Bay Area, as well as having enough money to see my kids through college, help them with a house down payment, etc., and be withdrawing at a low enough rate that I'd be highly unlikely to ever worry that I'd retired too early.