What about killing off girl embryos or blacks or obese, etc etc.
Are you suggesting that (presumably) white parents will be scanning their embryos to see if they'll turn out black?
While there may be some that do, I don't think there's any overlap between them and the ones who will be scanning for intelligence. Same for the ones who would select solely on gender or (again presumably) tendency for obesity, as that has a large component driven by lifestyle.
Is 15 IQ points a meaningful difference? How about 2 points? 30 points? At some point, it would obviously make a difference. Where that point is would vary from person to person. Part of the problem is that there are many factors that make up intelligence, and rolling them up into one number makes that number almost useless except in the most general sense.