I believe it is a personal choice for two consenting adults. It's funny as I'm watching a show currently, where a woman is giving a speech about how she was waiting out for marriage and didn't. Sorry off point but was just coincidental.
Personally, I feel that if this topic is linked to marriage then if it is an arranged marriage or not, having sex before marriage does not change that. Sex is a part of marriage but it is not a marriage. They will succeed or fail for various reasons.
I believe that it is each person choice. If they want to wait, that should be respected, if they wanna sleep with the person they have committed to in a non legal way that should be respected and if people want to sleep around well then each to their own. We all make our beds, (no pun intended) we make our choices and as long as we can stand by them without regrets then what another says does not matter.