Apple - Is this a normal fan speed and CPU temperature for an idle MacBook Pro (Retina, 15-inch, Mid 2015)

The various temperature readings look absolutely 100% fine!

This resource (which can be filtered) clearly shows that your CPU temp at 52.38°C is nothing to worry about.

My MBP temp is regularly between 66 and 81 degrees, and my fans are regularly at 6200 RPM when my CPU usage is high.

However, the fact that your stats indicate only one fan is spinning warrants further investigation. I would run an Apple Hardware Diagnostics to see if it finds any errors. To do this:

1. Fully shut down your MBP
2. Restart your MBP
3. Immediately press the D key and keep it down until you see the Diagnostics screen appear
4. Wait for Diagnostics to finish (this typically only takes a few minutes)
5. Once complete, one of two things will appear on the screen:
   • a No issues found message
   • a brief description of any errors found plus further instructions
6. If the diagnostics test does find errors, take a note of what they are

Note: If pressing and holding the D key at Step 3 doesn't work, start again at Step 1 and, at Step 3 press and hold both the OptionD keys instead. This will try and run diagnostics from the internet instead, so you will need to allow more time for it to complete.

Let us know how you go.