Are my MacBook Pro 2015 (15-inch) fan parameters correct? Are the fans on MacBook Pro 15inch always on? If so should they be audible when ear against keyboard?

I am not sure but I think my fans were not audible before but now I can hear them if I put my ear there.

Using istats menu I can see them running at ~2100 rpm left fan, ~2000 right fan.

The computer temperature is between 35-45 degrees celsius.

All I am asking are the temperatures, fan speed and subtle noise normal?
Fans, which contain moving parts, will certainly make some audible noise, though it's usually rather quiet and unnoticeable. Normal speeds should range from 1800-2200 depending on your level of usage. Intensive processes see the fan speeds go up to 6200.

For temperatures, idle activity should have temperatures at 40-50 ºC (CPU PECI die) and 30 ºC for air flow proximity.

If your fans get really loud and noisy, it may be a sign that your fans are malfunctioning or there could be some form of obstruction that causes noise when air runs over it. I'd check for dust and clean out any foreign objects found.