I'd say it all depends on your diet.
If you eat to bulk, you should gain the 15 lbs your looking for, as I did on my first cycle. Actually I gained 25, kept 15. I ate like a horse on this cycle and gained alot of bodyfat along with the lean mass.
I'm now in the middle of my second cycle of sus @ 500/week and due to my new job, I'm forced to eat less, and have dropped alot of bodyfat, probably about 3 or 4 %, but I'm about 3 lbs heavier on the scale, and my muscles are noticably bigger and more ripped, and the veins are starting to pop out in my shoulders. I have 3 more weeks to go, so hopefully I'll gain another 5 pounds or so of lean mass.
Diet is the key.