You didn’t mention how the lever feels when you apply rear brakes. If the lever gets solid instead of spongy, and it doesn’t pull too far in before getting solid, then you probably do not need to bleed the brakes. You might need to clean the brake pads (or lightly sand them) and clean the brake rotors. Then make sure you go through the break-in period like you would a new set of brakes. If that doesn’t fix it, then try a new set of pads.
If the lever is spongy, then it is time to bleed them or solve what ever problem makes them spongy. this wouldn’t be pads or rotor 99% of the time.