That code only sleeps the MCU.
The radio module needs to be slept as well. Initialize it and call radio.sleep() as seen in some of the
RFM69 library examples. If there is a FLASHMEM that also needs to be slept.
As a good practice, also check physical and solder connections, sometimes low quality flux (no pun intended) may cause unwanted current leaks, anything else attached that is using power needs to sleep as well.
And a third thing, although this should not really be necessary I would write a LOW to all unused GPIO.
Try these things one at a time and you should sleep at under 10uA.