Bedtime for 15yo

[PrettyCandles]

We have 15yo girl staying with us (my sort-of neice). What would be a reasonable bedtime for her?

when our DX's were 15 on school nights they went to bed 10.30pm. But during the scholl holidays and weekends they chose thier own bedtime, Someties they would choose to go up to their room and have lights off by 10.30 and at ohter times they sayed up until midnight, Usually in thier room though, Listening to music,reading or watching TV,

10.30/11

Or maybe you can say to her that she needs to be in her room by 10.15, and then lights out by 11.45 or something?

Thanks.