How have your lifts moved over the past few months? The reason I ask is that you are quite light for someone at 6'3" especially at 15% BF. I tend to think that, unless you're an ectomorph, which I don't think likely at that BF, you have a great deal of natural mileage left in you and it'd be inefficient to jump onto gear at this stage.
Natural training and an improved diet are probably all you need for at least another couple of years. Train to get stronger and the extra size will come so long as you are taking in surplus calories.