The stoner part of me that just hit the bong thought you thought those 15mg were 50mg hehe, but then the conscious part of me realized what you said.
This question I'm afraid I cannot answer
I have no experience with said 50mg capsules; I only have knowledge of up to 30mg and have never personally seen higher, although you must be like the sixth person I've seen to mention the higher mg (I think all said 50mg).
As I stated in the original post, though, it effects everyone differently. Maybe you aren't taking 100mg (the pills are lower mg than you think?). Try and find pics or some form of documentation of these higher mg pills.
Also... are you eating before dosing the Adderall? If so... how long before and what usually? How are you taking it? Are you crushing the beads inside and taking those orally (my recommendation)?
There are a lot of variables, man, but the majority of it comes from how it effects us person to person, and our state of minds as well. Even though that's a high dose it's possible for it to have more subtle effects on you than you're noticing. Just try not to think about it after you take it next time, and do it on an empty stomach. Again, though... try and find a picture or something of these higher mg.
But It's time for me to go... peace