Took me too long to edit the previous post, I got locked!
I have downloaded the XLP LowPower App note from microchip and it is helpful. The 14K50 does not allows for deep sleep, but regular sleep should do.
Obviously IDLE mode consumes 25% less than the normal run power, so I will have to make the Sleep mode to work while getting the PIC to resume from it. However there's probably something else that I have to find out, as 900µA seems to be abnormal for IDLE at 250kHz... I'll have to double check if the peripherals are also turning into low power too. I have also reduced the power supply to 2.2V (the regulator is able to switch from 3.3V for USB operation to 2.2V - TPS780330220 from TI). that should help a bit with consumption.
Could the I2C pullup be a problem? I have used 6.8k resistors which is pretty much the maximum, at 10k and beyond the operation of the I2C bus is unstable.
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