2015 Acura RDX: What is the oil type and capacity?

Each trim level and options package of the 2015 Acura RDX comes with the same 3.5L V6 engine -- J35Z2. So no matter which '15 RDX You're running, You'll always require the same 4.5 quarts with filter (or 4.2 quarts without) of SAE 0W-20 full synthetic motor oil. In its absence, You can potentially substitute SAE 5W-20 in the short term, but this isn't recommended, as You'll be adding undue friction into the engine's operation. This can be a problem, especially over the longer term. Friction can and likely will lead to premature wear and tear, and an early engine failure. Therefore, even though it may cost You a bit more, don't try to cut corners, because You'll only be hurting Yourself (and Your RDX) in the long run.