By 1929, Ford has built 15 million cars.

It would be OK in a context in which the present tense is being used. "Fifteen million" would be better.

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An example of such a context would be a narrator of a video documentary putting himself back in time and telling the Henry Ford story as it happens while pictures of each event show on the screen. For instance:
In 1863, Henry Ford is born on a farm in Greenfield Township, Michigan, (video shows old house and parents). In 1879, Ford leaves home to work as an apprentice machinist in Detroit, (show pic of young Henry about that time). By 1929, Ford has built fifteen million cars, (show factory with cars coming off the assembly line and auto showrooms).

Otherwise, in the normal context of the writer or speaker looking back from the present, the sentence should read: By 1929, For had built fifteen million cars.

By 1929, Ford had built fifteen million cars.

Thanks to all of you.