No, not if you're in the appropriate amount of pain to warrant Oxycontin.
Pain causes your dopamine levels to drop. Oxycontin raises your dopamine levels. The dose prescribed being in accordance with how much pain you're in, taking Oxycontin, your dopamine levels are raised to a level similar to when you're not in pain, which tricks your brain into thinking you're not in pain, into not feeling the pain.
The problem is when you take Oxycontin when not in pain, or when you take a higher dose of Oxycontin than your pain warrants. That's because when you do that, the Oxycontin raises your dopamine levels to above what's normal. That leads to euphoria, contentment, and feelings of well-being beyond what is emotionally appropriate for the situation, thus causing you to not care about things that would normally bother you and not feel any pain, not even pain you normally feel.
That's nice. Why wouldn't that be nice? So you do it again. It doesn't take long doing that that your brain starts adjusting to those higher levels of dopamine as your new normal, which then drives you to seek even higher doses.
What's not nice is when you stop taking Oxycontin. When you do, your dopamine then drops to their natural levels, the levels your body naturally produces. The thing is, that's so far below what you've made your brain think your new normal is that it feels not just psychologically painful from losing that euphoria but physically painful as your brain thinks you are in pain, the reverse of the illusion taking Oxycontin creates when you are in pain. While there is no nerve source for the pain, your brain thinking it's in pain results in an overall malaise, a sense that pain is emanating from everywhere in your body at once but nowhere in particular, and it becomes intolerable, as intolerable as the extreme pain that led to you taking it in the first place, or more so if you've since increased your dose to try an maintain that level of euphoria, something called "chasing the dragon."
Taking 15mg of Oxycontin one time when you weren't in pain for most people doesn't cause you to get "addicted instantly." I say "most people," though, because about 10% of people have a genetic or psychological predisposition to addiction called "addiction disorder," which they may not even know about as it lies latent until triggered by something that brings about such euphoria, which may still go unnoticed if they don't have the means to duplicate the euphoria but spirals instantly into addiction if they do.
As for withdrawals, if you take Oxycontin while you're in pain and then ween yourself off of it as your pain subsides, you have no withdrawals because your dopamine levels remain constant. HOWEVER, if you take Oxycontin when you're not in pain and raise your dopamine levels well above normal, you will experience withdrawal symptoms even the very first time you take it, those withdrawal symptoms being what is commonly called a "comedown." You're coming down off the high. What goes up, must come down. That's withdrawal. It happens every time. Addiction starts by chasing that high, but it digs its claws in and takes hold as you transition to chasing away the comedown, chasing away withdrawal. Like I said before, if you have a predisposition to addiction, either genetically or psychologically or both, then not being able to tolerate the comedown, the withdrawal, happens the first time and the addiction manifests as you then take more Oxycontin to stop the comedown, stop the withdrawal symptoms, and try and return to at least as high as you were before.