The 15700 is a PCIe bridge and PLX chip with some signal conversion capabilities it was never even designated as a wireless chip heck we have apple’s manuals:

338S1186 1 IC,BCM15700A2,S2 PCIE CAMERA PROCESSOR U3900 CRITICAL

5 digit part numbers are Broadcom’s “IP bridge SoC” the BCM15900 on the iPAD pro for example handles the eDP connection with the screen IIRC and the digitizer function.