Development means that the code is optimized - it’ll run faster, but you’ll have a hard time debugging.
DebugGame only optimizes the Engine code. Your game code can be debugged.
Debug means that nothing is optimized and you can debug the Engine code. This will run the slowest, but let you step into the Engine code.
I am still a newbie myself, so I’m afraid my ability to help you is very limited. Personally, I build in DebugGame Editor and it only builds my game project in a few seconds. Perhaps someone who knows what he’s doing can give you a better answer?