Need Help Coming Out ?

I'm only 15 and I know definitely that I'm gay and I'm having a tough time figuring out how to come out to my mom. See the whole thing is she is kind of ok about gay people but then there is part of it were she doesn't like them (Guys who talk w/ a lisp). So what do you do with a parent who has mixed opinions? I don't really know if she is one of those parents who doesn't suspect their child as gay, I've never dated a girl because I just can't.