As much as we have grown to love them over the years, we should keep in mind that the Caliber 15 movement was designed as an economy movement, and specifically to offer a less expensive chronograph than the comparable Cal 12 models. [the page below, from 1972, illustrates the price differential between a couple of the Cal 12 / Cal 15 pairs]. Accordingly, the Cal 15 movement:- used a brass balance wheel in place of the Glucydur balance
- used the Kif shock protection system, in place of the Incabloc system
- deleted all the parts and assembly work required for the hour recorder.
I have to imagine that in the era when Heuer was producing these Cal 15 chronographs -- 1972 through 1979 -- if they had extra Cal 12 cases sitting on the shelf, they would have been happy to use these cases to house the Cal 15 models . . . a less expensive approach than ordering a fresh batch of Cal 15 cases. This may help explain why it is not uncommon (or too suspicious) to see the Cal 15 chronos using the Cal 12 cases.
Jeff
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: I have to agree with the other posters that a 1533 in a 1133 case
: is not uncommon. I have seen quite a few of these over the years
: sometimes on one owner watches. It's hard to comment on the dial
: without photos, but I wouln't rule it a problem just because of
: the case
