I don't think you are being too conservative, you just have high moral standards which is very commendable nowadays. In your house, you call the shots. If you aren't comfortable with allowing your son to have his girlfriend over, then stick to your guns and don't allow it. You are his parents, not his friends. Look at it this way, if she got pregnant, you probably wouldn't hear the end of it for years to and somewhere down the line, you'd be blamed for it . Someday, he'll be grateful to you for your rules. I know alot of parents who were in a similar situation, and years later, the kids respected their parents for having tougher rules. Unfortunately, the age of consent is 16 and if his mother allows sleepovers with the girlfriend, there is not much you can do because you can't call the shots at her house. It sounds like this girl's parents need a reality check on teen sex. Many parents feel that it's better to have the kids do "it" in their house rather than sneak around. If he were my son, I would sit him down and openly talk to him about safe sex, pregnancy, STD's, not to mention sexual offenses.
M.