nRF24L01+ RX in pulsed operation to save power?
Look into how much the module is consuming now.
If it is consuming a fraction of the whole system power, it may not be viable.

Check if you can disable TX of the receiver to save some power.
Run the MCU using watchdog so that it wakes up, does the job and sleeps again.

To sync communication, send a request packet from the receiver to the transmitter for every update.
In that way, you will not be transmitting when receiver is offline and expecting trial and hit packets; receiver controls the flow.
By changing the frequency of requests, you control the frequency of updates and power consumption.

Thus, in the most optimal way, use watchdog timer to wake up MCU.
After wakeup, enable the receiving module (both RX and TX if they can be controlled separately).
Send a request packet. Wait for the packet with a timeout.
If a packet is received before timeout, use it for the update and sleep.
If timeout occurs, sleep.