This does not exactly answer your question but it may help. I was working with plywood and the 1515 profile over the weekend, I wanted panels that were inset on the sides/rear of a cart and proud on the top like an MFT top.
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The slot in the 1515 series is 8mm, so each of the other 2 legs of that profile are 15mm, or near enough. If you were using 3/4" nominal plywood (18-19mm), and wanted it to be flush on the outside/top, you could route a 3-4mm rabbit in the edge to make it 15mm thick, then screw an 8mm strip to the underside (rabbit) and fit it into the slot.
Hope this makes sense.
RMW