Every 15 year old has heard plenty about Sex. It is constantly going through their mind, they think about having it with a variety of Partners, some are even having it.
Any Parent tarding about their Teen reading about Sex in Literature is 6ish years late. If your Kids peers haven't "informed" your Kids about sex, they have been finding their own sources, without you even knowing.
...and that's a Fact.
Have you already forgotten what You did as a teen? Unless you were sheltered to the point of abuse, you had a working, although likely inaccurate, model of what Sex was by the time you were in your early teens.