You're lying to yourself. You're not over her and detached after just 15 days, from here it looks like you're angry and hurt and not in a state where you can have emotionless sex with an ex. People here have been in your situation many times and speak out of experience. You've gotten great advice in the thread, read it again. If not, you've to learn the hard way and that is maybe the best teacher in this case. Good luck, but be careful to protect your heart.