Win10 uses a new(er) Windows Defender anti-virus/security program. Honestly, unless you are using your computer in a commercial/business capacity, it is all you need for anti-virus protection (yes, it's that good now). Run Malwarebytes, Spybot Search & Destroy, and CCleaner OFFLINE once a weak to "clean up" the rest of your computer (DON'T run any of those 3 real-time...you don't need to and they will just slow things down arguing with Windows Defender).
As a minimum, what you may need to do with your new Win10/Windows Defender install right now is set all new Exclusions in Windows Defender for anything and everything relating to your flight simulator. If not, Windows Defender is "inspecting" every single flight sim related file you are loading when you start the sim...and when you are using it too. Choke, choke, choke your flight sim performance.
Windows 10 is not the problem to everything that happens on your computer. I really wish people outside of the IT community would learn that. Almost all problems are the end user not having done the proper setup to make everything run at it's best performance.