Measuring the Raspberry Pi power consumption
If you use an ADS1115 and power it from 5V you can use two differential inputs on the ADC to sample both sides of the current sense resistor.  You should use series resistors and a filter cap on the current sense as the current waveform for the RPi will most likely have components above the 860 sps limit of the ADS1115.  Design your low pass filter for at most 860 / 2 cutoff (remember the filter cutoff is only the -3dB point).







simulate this circuit &ndash; Schematic created using CircuitLab

The ADS1115 MUST share a common ground with the RPi in this configuration.  

Note that there are a few issues with this which will limit accuracy.  A much better circuit would to be to use a current sense amplifier with integrated ADC like the TI INA226.  Maxim and others also make parts that will work, some including the current sense resistor (or hall element) inside the package.

EDIT -  For the ADS1115, the ground connection to the RPi should be short and direct, not something round-about through the USB connection to a PC providing power for both.