15mg/day for both the female tiny dancer under 100 lbs and also for the male over-6' chunky brute? Yes, I'm purposely driving to extremes in order to show that different people would absorb and use different levels. Other factors include residual capacity of the Adrenals, intestinal permeability, stress in one person's life vs. another, etc..
Bottom line, I do agree with Orion that 15mg/day for the average person, and to remain wary of any overdose dangers. But doctors and their patients need to determine how "average" any given patient is. Right from the start, the doctor is going to consider his/her patient "average," whereas the patient will consider himself/herself not average, inciting a built-in tension.
p.s. I'm right at 100kg, taking 25/15/5 = 45mg... and just barely making it from day to day. Yes, I read the dutch study about men on 45mg more prone to osteoporosis and therefore had a scan last year. My last point is... I'm at 45mg and do not have any of the symptoms of having too much cortisol. Not that I want to get there... just want the optimal level for me and for how my body is behaving right now. Others might be taking half of what I take and for whatever reason it is too much for them in their case and they end up meeting Cushing.
The better part of wisdom is to know when to trust a single number and when to broaden the range, keeping ever aware of what might happen if you're too high or too low. Don't adjust based on the number only. Adjust based on what your body is telling you, within a reasonable range of the number.