There should be very little latency with this setup because I am not doing digital transmission here like using WiFi or similar wireless protocol.
The TV video output from the Raspberry Pi is directly fed into an analog wireless video transmitter, then analog wireless video receiver is used to get the video signal and display it on screen.
To check the latency of RPi FPV system I set up the Raspberry pi with a camera pointing at my computer and had a phone ready to take a picture. On my computer I started an online timer and captured a few photos to see how long it took for the whole setup to display the captured timer.
Here are some of the latencies encountered:
From a few other tests and from these images I was able to figure out that the delay was 8-60 milliseconds while recording video on Raspberry Pi. In my opinion that is good enough to fly a drone at low speeds and still be able to respond on time to avoid obstacles.