I don't think that night time is out of the question at 15, as long as it's not a school night but I am pretty tough on time frames.
If my teens wanted to go to dinner and a movie, then the time frame fits that. It does not include time for just hanging around and loitering at shops etc. I double check the movie times online and allow 15 minutes before and after. This does not include time for walking to McDonalds after the movie and hanging out there either.
I do think there are times that you need to be one step ahead of teens though. A few years ago now DS2 was very insistent about a particular pick up time. This was enough for me to be suspicious and come back 30 minutes early. It turns out he'd been picked up from the movie theatre, by another parent and taken elsewhere. To this day I have no idea if the other parent knew that she'd been part of a plan or not, but the fault was with my DS as far as I was concerned because he certainly knew what he was up to. They had only gone to another restaurant up the road so I have no idea why he didn't just ask, but anyway, you should have seen the look on his face when the parent delivered him back and I was there waiting. He's 21 now and certainly still remembers it
So, night time outings on weekends, not out of the question but with strict limits and no just hanging out at the shops or around the streets.