My girlfriend wants to have sex?

now, i am definitly not gay. i love women. we are both virgins. i always thought to wait for marriage when its safest to have sex, little chance of disease, and if pregnancy occurs, we are married and prepared for it right? my girlfriend is 15. i am 17. yeah i know what your thinking because i would think the same thing. but she is far more mature than anyone i know and she really wants to have sex with me. but i dont want to make any hasty judgements. we have been dating for six months. just.. i dont know should i have sex with her? not only that but how effective are condoms and birth control, because i would use both before i even thought about having sex with her. i was also thinking of spermicide but it could have side effects that might be bad. so just.. general opinions? and make them intelligent please