As mentioned before, the Cheetah X15 can almost be called a quiet drive, considering that it runs at an extremely high rotation speed. In Idle mode, the drive never exceeds the noise level of the the two 10,000 rpm drives.
The levels of access noise are generally lower as well, but it sounds very aggressive subjectively, and the noise can only be reduced if you install the drive in a well-insulated case. However, since the Cheetah drives are not meant to be used in desktop systems, the noise factor is not as much of an important consideration.
As expected, the drive clearly becomes hotter than any standard desktop drive. Due to the high friction at 15,000 rpm, it will quickly exceed the temperature of 58°C that we measured after ~30 minutes.
In any case, you should generally make sure that every drive running at 10,000 rpm or higher is properly cooled. Even if the drive might run within an acceptable temperature range, you can definitely increase its lifetime by cooling it.