Speeding up KSP loading for faster iteration

Since most changes to code or content requires restarting the game, it helps a lot to make loading times as fast as possible.

You can strip out a lot of unnecessary features to make KSP load faster for mod development. Some folders you can usually delete (unless your mod will need them):

• KSPedia
• Missions
• Spaces (IVAs)
• Props (Objects used in IVAs)
• zDeprecated (Old parts, some old vessels may not load without)
• Some content of Parts, whatever you don't need for testing
• Agencies May cause minor issues
• Flags, FlagsAgency and FlagsOrganization May also cause minor issues

You should also delete any stock parts that you don't need for testing your mod, as well as the DLC folders.

You can also install the QuickStart mod to have the game automatically return to the scene you left it in: https://spacedock.info/mod/110/QuickStart

Additionally, installing KSP Community fixes will speed up game loading through its caching functionality. Keep in mind though that it changes a few stock behaviors, I would recommend reading the list of features: https://forum.kerbalspaceprogram.com/topic/204002-18-112-kspcommunityfixes-bugfixes-and-qol-tweaks/