Select sampling frequency to closed loop control in a DC-DC converter
You only need to consider the Nyquist frequency if you want to be able to fully reconstruct your sampled signal.

Do you want to fully reconstruct the shape of the inductor current ? I think not, you only need an average value of the coil current. So if you time-average that current (this can be done by using a filter) you then only need a much lower sampling rate to measure that average. As long as that sample rate is sufficiently faster than the speed of the DCDC converter's voltage or current control loop it will work fine.

Notice how the converter's switching frequency does not directly relate to the speed or sampling rate of the control loop !