To me, it would depend whether, with hindsight, you feel this man was (is?) a sexual predator with an unhealthy interest in underage girls, and how that manifested itself.
My opinion would be very different if he was, say, 20, and just ended up with a younger girlfriend, or if he was, say, 35, which would point towards really inappropriate behaviour. If you were groomed, or pressured, that too.
If it were the latter, then to be honest I don't think I'd have encouraged a relationship with her father at all, but that is of course easy for me to say as an adult woman, who doesn't know this man.
The long and the short of it is that, whatever the individual case, in general I would have concerns about a much older man who had the judgement and inclination to have sex with a 14/15 year old, and I would be concerned he could repeat that inappropriate behaviour with another underage girl.
My behaviour surrounding the relationship and information your daughter has here would have to be informed by that.