Are you on a laptop, or on a desktop with both “integrated” and “discrete” graphics?
Chances are, your driver has white-listed the editor, and runs that on the “discrete” graphics card, but hasn’t white-listed the built game EXE, so that ends up running on the “integrated” graphics, which is a lot slower.
Exactly how to fix this depends on your particular system – both the brand of the graphics/CPU, and the brand of the system itself (because often this configuration is part of some shovelware.)