I don't think it's unrealistic, I know many teenagers that are not having sex, and have more self control than to. Geez, people, we are NOT wild animals!
I was 24 years old when I had sex. Many of my friends CHOSE to have sex, but they did not *have* to. I CHOSE to wait for my husband, and I did without a problem. It was NOT THAT HARD.
That being said, I believe it's unrealistic to ASSUME all teenagers are going to wait, and not offer them the facts. My mother, at age 15, told me all about the different means of protection, and was very open with me. Though I told her I planned to wait, she still wanted me to know what was out there and know that I could come to her for a GYN appt and she would not judge me or lecture me. She even confided that she CHOSE to have sex with my dad before marriage.
I plan to do the same with my children. Share my own exp, encourage them to wait for their spouse, but also offer the facts.