Klipanos as patro said above you cant compare Luxrender with mental ray or vray
Though if you start digging into luxrender settings and become a bit familiar with them im sure you can have better results much faster, for example in an exterior scene i would use as surface integrator --> path , if i had an opencl compatible gpu i would use hybrid too (to use cpu and gpu at the same time) and also depending on the complexity of the scene i would tweak the light depth, etc.
Also there are a lot of "tricks" about not using extreme material values (which take much longer to calculate) , etc.
You can check in the wiki some of the tutorials which though they are made for blender, im sure you will be able to apply them on 3ds max since all properties have the same names.
Finally pls be one of the few 3dsmax users that posts his work on the WIP thread where we can give you more specific advice, since we will be able to take a look at your scene