I can't find in the datasheet what is the maximum noise density that you can have on the supply to achieve the datasheet performance.
How can I find this information? I don't want to use an ultra low noise LDO if not necessary.
Does 150uV RMS is ok or I need something below 50 or even below 10uV RMS?
This is a difficult question to answer because it is a function of the noise coming from the power supply and the power supply decoupling caps that you use. And I'll say off the bat that I don't have a quantitative answer for you. We generally measure these devices with lab power supplies (e.g. Keysight E3631A) and have no trouble measuring 1-2 dB noises figures with these. These supplies would have relatively low noise but they are not super low-noise boxes. I just looked at the noise spec (for E3631) and it says "<350uVrms/2mVpp from 20 Hz to 20 MHz". If this is equivalent to the 150uv number you are referring to, then that LDO should be ok.