HH,
Given their relative flight profiles, and employment, how much of it's fatigue life does a B-52 use up in a year compared to an F-15?
Also, given that aircraft tended to be "over engineered" in the 50s and 60s, and that weight saving was presumably less of an issue for the B-52 than the F-15, perhaps fatigue in general is less of an issue for the B-52?
Just a couple of thoughts - no doubt someone more informed will be along shortly!