Upgrade to Delta Reserve?

Any advice?

I’ve been with AMEX for a while, and got rid of all my other cards except the Platinum Delta card. My wife and I fly fairly regularly, mixture of work and pleasure, usually about once a month, sometimes twice.

I got an upgrade offer (15k miles). Just wondering if it’s worth the AF. Wouldn’t mind the lounge access at our home airport (BOS).

Thanks in advance!