3 sets of 15 reps ????
I like doing 3x10 & 2x5 to failure on each set... the 2x5 is like showing the muscles what they will be lifting for 3x10 in a couple of weeks..haha
The idea is to hit slow and fast twitch muscles...build some stamina, quick strength and mass, I also train isolation which isnt in fashion anymore, I dont think training that way in compound exercises would be as affective or safe.
O'kay, Scotty has answered already ^^ I share that interest in how to mix things up and found out there's really a lot you can do and nothing's wrong! I've read about pyramid and reverse pyramid sets, check out those too if you want :)
Hey, you just do whatever is comfortable..start out with 5 our 10 lbs 3 sets of fifteen if you complete that and it seems too easy, add weight another set, or more reps. With more reps you will get endurance, with more weight you'll get your strength!
There is no "correct" answer without an assessment or the guidance of a certified PT to guage your overall fitness level before starting any program.
The most common rule is: to build size = lower reps (2-5) with more sets (6-8), to get a more lean look = more reps (12-15...or more) with lower sets (2-4) and to build strength you will fall in the middle, 3 to 4 sets with reps in the 8-12 range (which is where you typically want to start).
Regardless, starting out with weights you will see an increase in size as your arms are adjusting to the loads you are putting on them (building muscle). If you do not want to get to "big", then simply decrease the weight and do more reps. If you are happy with your size and want to look cut, then simply do more reps with the same weight.