Just run a basic cycle,
Week 1-12 Test E @ 500mgs/week
Week 1-5 Dbol @ 40mgs/ED
Your "goal" of 15-20lbs is a 110% realistic with this cycle. But, the ball is in your hands.. you have to provide the hard work and dedication with diet and training everyday. Make it a priority. I would guess, if you had a solid diet/training/recovery time, you could gain 25-30lbs, probably keep 80% + with a solid pct. BUT I have no clue who you are and what level you at with bodybuilding.
*Liv52 for liver support. Clean diet, with surplus of calories. Diet is what determines your outcome. It is the heart of a cycle.
AI, Armidex @ 0.5mgs, when needed. For water weight and other Estrogen related sides.
Then if your looking to cut next cycle, or future cycles then run a solid cutting cycle and throw a nice stack in there, at this time you will be more educated and a lot more experienced.