Well, many 15 year olds (and younger) are sent to boarding schools in different countries/on different continents. Not so much from the UK but definitely to the UK from elsewhere.
And even when boarders are in the same country, they don't necessarily see more of their parents than international boarders/than you could possibly manage to arrange. Christmas, Easter, summer hols and possibly for half terms as well - either them visiting you or you them.
So anyone happy with boarding school should consider this feasible.
The older kids are at the 'going off to uni' age anyway, what if you stayed and they end up rarely coming to see you? Because their social lives /jobs take them away during the holidays and they're busy all the time, you might only see them 3-4 times/year anyway. And you'd find yourself wondering why you stayed for their sakes.
I moved to a different city at 15, on a sort of weekly boarding basis, though I had a busy social/sports life so ended up not going home many weekends at all. Maybe that's why I never got into teenage arguments with my parents. I simply didn't see them frequently enough, and when I did, they treated me with all my favourite things ;)
Though as you are thinking about a permanent move: I now permanently live in a different country than my parents (it was my choice/my move though) and find that of all the phases in my life, I now more than ever miss my parents being near. As a grown-up with my own family, rather than as a childfree couple, or single young adult, or teenager. If I were in this situation due to my parents' choices, I'd be a bit miffed (whilst respecting their life choices of course).