I had very long compilation times. Robert suggested to eliminate the Vulcan .vh include files and to define VO-like constants in a basic dll and then to insert this basic dll as a reference to the Dlls.
Indeed this was the reason: Working on several hundred files with 1 to 3 includes made compiling slow. Now the compile times are good, even with some remaining includes.
What I could not resolve: The .rc files still contain the include
But this is secondary for the moment for me.