I’ve been doing more reading, and there seems to be two methods of converting a front 15mm thru to 12mm. End caps comes up a lot. But for some, like White Industries, the solution seems more robust:

The Mi6, CX11 and CLD can be converted to accept a 12mm thru axle assembly for frames designed specifically for the thru system. Conversion kits replace the hubs internals to allow for the 12mm thru axle that is supplied with the frame. Upon request, the hubs can be outfitted as 12mm thru compatible at the time of purchase.

I’m not mechanically inclined, but I would take more comfort in the solution above to sticking end caps on a 15mm hub (which will be receiving a 12mm TA).

Am I on the right track?