our 15yo is old enough to babysit themselves but also old enough to wonder where we go til 2am

so we hit this awkward inflection point this year. F44 dh 46, kid is 15, only child, very independent. weve technically not needed a babysitter for a year now, they can absolutely make their own dinner, lock the door, do homework, be fine for 4-5 hrs in the house alone. great in theory. except now were having to explain ourselves to an actual semi-adult who notices things. our old sitter (gods bless her) just took the money and watched netflix. our 15yo notices what time we leave, what time we get back, what i wore, that we both got dressed up, that we sometimes come back from a hotel on sunday morning instead of saturday night. a few months ago they asked, very casually, very teen, "where are you guys even going every weekend, you used to be so boring". and i laughed and said "ah you know, mum and dad are reclaiming their youth, we go dancing" which is half true. but they then said "oh which club" and i had to make up a place name and im pretty sure they googled it bc the next morning they were quiet. i dont want to lie more than i have to. i also obviously dont want my child to know what their parents actually do on saturdays bc... no. that is not appropriate info for a 15yo about their parents under any circumstance. how do other ppl handle this transition phase. when your kid is too old to fool with a sitter but too young (and frankly its NEVER appropriate w your own kid) to know whats actually going on. do you cut back? do you double down on a cover hobby? do you just go to hotels further away so the "coming home at 9am" thing is more obviously a "weekend away" thing?