this sounds like a memory leak, which im pretty sure the game doesnt have (everyone would see it constantly if it where), we fly 3+ hours twice a week in a group and my pc uses the same memory thru-out, tested along with several other people multiple times
i will test again tonight since that will be the first time for our group flight in su9 but i dont think this is a new issue either (see the linked post that has the same issue)
some people have had success fixing this issue disabling the NDU
this one may be worth checking out, it turns of the data monitoring for metered connections
this one just confirms the same thing with an unrelated source (not game related)
https://blog.pcrisk.com/windows/12971-fix-memory-leaks-in-windows
i advise you to do your own research before attempting any of this
having said that i made this regedit around a month ago (not long after that post) testing for someone else
i did not show any memory leak but i have not seen any adverse affect from the edit