I have a partial answer to the "What's the current status of efforts to get the DPA MMA-A working with an iPhone 15?" answer.
I have an MMA and use it regularly with my iPhone 13. This week a buddy of mine let me play with his new iPhone 15. Here is what I learned.
A standard USB Micro to USB C cable connected between the MMA and the iPhone 15 did not allow the DPA app to see the MMA device. The DPA app was basically locked out and no controls worked. However, when I then launched the Shure MoTiv app that app did register the MMA device and the mics plugged in. That set up though uses the default mic pre settings on the DPA app, so the gain was by default set way too high for a high SPL concert recording.
I tried the same test using my regular DPA cable and a lightning to USB C adaptor. Exact same results. The DPA app didn't see the MMA, and therefore I could make gain changes, select filter presets, or engage the filters. But again, downstream, the Shure Motiv app recognized the external USB device and I was able to make a clean recording. Unfortunately though, the gain is set to high in the DPA app by default for this to be a workable solution.