After doing first optimizations, I've looked to code inefficiencies (like some shapes are built twice: once in preview mode and another time as final mode, but they rebuild the very same shape). in the code flow in events passing to get the "last 10%" from speed improvements. With those changes, the code works with an order of magnitude faster, if you will work with a medium/large shape number. The single two slow things are the OpenCascade code (which may not be that slow, but it have it's contribution) and the autosave option if is enabled.
Some other issues will be fixed and if regression will be found, they will be also be fixed. But at large, you will like to work with NaroCAD with many shapes as it will feel instant, even much faster than older Windows Forms versions.