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Part of its lifespan depends on what kind of tuning it has, with some commercial engines being detuned for longevity instead of power output, and if it has extra optional features like additional oil or transmission cooling, or bypass oil filters, and other extras. Consumer vehicles however are often built and designed with lower lifespan expectations and a higher performance profile.

But ive had numerous 90s+ low trim consumer vehicles breaking 300k miles easily and I know some semi-trucks do have 1 million+ miles on the original motor because of such features. And so while I don't have much experience with commercial delivery vehicles, I don't see any big problems with saying they could go a million miles themselves, although due to the nature of delivery driving and driver turnover I would also expect 400-500K miles to be when a rebuilt should be considered unless it was all done by one driver who doesn't drive like mad and they had skilled mechanics maintaining them. And if they didn't care about ruining the engine at some point I would expect 6-700K atleast if it was a well built commercial engine with commercial features.