I can confirm. The latest firmware consumes 7.2uA in sleep mode. I took plain RAK811 module, connected to it using UART and issued command AT+SLEEP.
When the power voltage is 3.3v power consumption should be ~9uA. At 2.6v power consumption ~7.2uA.
If reduce the voltage further the module stops working although according to datasheet of stm32l151 and sx1276 the minimum working voltage could be lower. I think that's because there is an LNA IC on the board that has a limit of 2.6 volts.