The low MCU activity implies there is not much processing (application or other peripheral data) going on when the radio is receiving. The 1MHz clock allows for about a 1-1.5mA current savings over the higher speed 32MHz clock.
The 14.7mA number is the total current consumption of the chip in that setting and not only the RF front end, even though a large chunk of that number is the power consumed by the RF front end.