Problem: The engine compiles every time we do changes to our project

I guess Unreal Build Tool doesn’t care about the Visual Studio solution. The “Build” command, as it is declared in the project properties, invokes UBT with no argument telling which VS project to build (it passes the path the the *.uproject file).
What really affects compilation time is bUseUnityBuild property of BuildConfiguration class. It dramatically decreases compilation times in case of small changes to the sources.
I will try to repeat the sequence you offered and reply later.
Thank you for the response =)