It sounds like you already know the answer. My 2 cents is to back yourselves for another month or two, keeping it lean. Use the time to improve the viability o

It sounds like you already know the answer. My 2 cents is to back yourselves for another month or two, keeping it lean. Use the time to improve the viability of the business, but also to shop for other offers. A bit of competition will increase that valuation and let you assess the quality of advice and commitment you'll get. Alternatively sell him 15% of the company at the valuation he is offering now, and use that money to keep going until the next round at a higher valuation based on more mature business results.