How much do you weigh? You will definitely feel that. I don't know why you would get sick. Make sure you eat something. Eat a hamburger with bacon or something high fat. IMHO experience taking Oxy with a high fat meal makes the blood content level much higher for maximum pain relief. You may start nodding off so I would suggest not driving.
God I miss the days when 3 5's would touch me. I"ve used H once and took percocet maybe 4 times in the last 18 months. And still I would need more than three 5's for sure. But for a new user I would say try 5-10 at first. I saw my buddy get fucked up on 60mg of codeine when he had his tooth taken out. You never know how your body will react.
You will be fine with 15 mgs.. unfortunately now days some of us have climbed up to a 100-150 mg dose (ofcourse thru CWE). All I will say is kick your feet up and enjoy something that you will be chasing for a long time