Im going to go out on a limb here. And say IF your body man actually does give you an estimate. Chances are it will be an open ended estimate.

Any good metal man knows , rust spreads. Once you open it up this WILL get worst. Been there , done that

Im not a body man, but Ive done enough body work to know 15 hours isn't going to be even close to fixing this. Let alone paint work included.
One thing Ive learned working for myself and on old cars, the labor and time guides are useless. There's no such thing as flat rate on old cars. At least not in my world
just my