I like to hit all the rep ranges in the same workput when going for mass. ie, heavy sets of 5 reps on squat, followed by higher rep sets 8-10 on hacks or leg press, this has worked well for me.
Just my .002
If I was you I would only use other people opinions on rep ranges as a base point for your workout.
If I were you I would try one set of rep ranges for 4 consecutive workouts and if you feel like its doing you good stick with it for a while but if you feel like your not responding to that particular rep scheme change it about and stick with the new scheme for 4 weeks. Eventually you will find a scheme that is perfect for you.
Keep this in mind Dorian Yates only did reps of 8 for 2 sets for all leg exercises where as Ronnie Coleman goes up to 5 sets and 15 reps for his leg workouts. Different people respond differently to different things.
20 rep squats do kick ass sometimes. But its not the best way to train all the time.
Your legs do 100s of reps each day (walking). So hight reps wouldnt surprise them. But heavy weight, really heavy would!
15+ reps for LOWER BODY??? Geez I have to lift 40% of my 1 rep in deadlift to even come close to 15.... Gee weight training is supposed to be lifting HEAVY WEIGHT! Not light weight pumpin'