"would you marry a woman who had slept with 15+ men?"
Based on the non-existent context, it's hard to answer this question.
It would depend upon many things, based on this sole premise of number of sexual partners, I don't see why not.
More factors need to be considered such as: Why has she had sex with 15+? Is it because in the past she flung around? Did this happen in a short time span and time has gone on enough to show this most likely just a phase? Or perhaps was it over the long-term, due to bouncing from numerous relationships and one night stands? This would indicate a lack of commitment and indecision to not make marrying a safe option.
A number of sexual partners alone should not dictate this decision, essentially like saying "would you marry a women who ate 50 kit-kats?". But then you hear those 50 kit-kats were yours and they were stolen from you stash of kit-kats, now you have a problem friend.