As you can see in the chart above, the Miyota caliber 9039 and 9015 are nearly identical with exception to two main differences:
The calendar complication
The height of the hand stack
The most notable difference when the 9039 and 9015 are compared is that the 9039 does not have a date option. The 9015 is available with 3 date options. This is not to say that a watch with the 9015 has to have a date. Before the 9039 was introduced, watch brands seeking to design a no-date timepiece would simply cover the date wheel with the dial. This Borealis Olipsio is a good example of using a 9015 without a date aperture cutout in the dial – now they can just use the 9039.
Because of the lack of a date setting position, the crown on the 9039 only pulls out one click for time setting. The 9015 has two time setting positions: position 1 for adjusting the date and position 2 for the time.
This is why using a 9015 without a date is not ideal because it will still have the calendar setting position and functionality.
Hand Stack Height:
Another difference between these two movements is that the 9039 is capable of being used in a slightly thinner case than the 9015.
9039 minimum case thickness: 8.25mm
9015 minimum case thickness: 8.6mm
The has lead the watch community into thinking that the 9039 is a slimmer movement, but in fact they both have a height of 3.9mm tall. The reason the 9039 can fit in a thinner case is because the hands are lower than on the 9015:
9039 total hand stack height: 1750µ (1.75mm)
9015 total hand stack height: 2100µ (2.1mm)
Handstack comparison from Miyota:
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The 9039 is essentially a low-hand height version of the 9015. These movements could possibly be interchanged as long as the case can accommodate the differences.
The dial feet location is the same on both movements:
Interchangeability is not guaranteed and needs to be researched further, ie: stem length, stem height, etc.
If you have successfully swapped these calibers (or even attempted), please comment below.