When you say 70-80dB, is that using a sound level meter to measure at close to the driver? That's insanely loud TBH. My comfortable level is less than 50dB measured at around 1cm from the driver.I don't own the DT770 so I can't do the comparison, but the SRH-1540 can be fatiguing if you play at very high levels. At moderate to high levels they are fine. If you are the type that always listens at close 90db or more then you should probably skip the 1540. Personally I don't find them fatiguing for my use case which includes many different types of music, but I mostly listen in the 70-80db range with headphones.
Remember the decibel scale is logarithmic, that means for every 3dB increase sound energy is doubled, for every 20dB increase sound energy is increased by a factor of 100.
Look after your hearing...