How do you transfer your old version project into a newer version of UE4? (4.15 - 4.18), is the process risky for your project because I would seriously not appreciate all my hard work of months to get glitched up and show errors inside the newer version of the engine.
When working with the engine, even if it’s on the very same version, I make 2-3 copies of the project a day, and store the last 10 copies on a separate SSD dedicated to just doing that. Definitely make a copy before you transition.
Oh yeah, it’s risky. Depending on how complex your project is, you’re almost guaranteed to run into issues. So much has changed since 4.15. The Blueprint Compilation Manager introduced in 4.17 and vastly improved (too early to tell, tbh) in 4.18 may still give you issues - consider turning it off as a last resort.
Once you launch a new version of the editor, you can open an existing projects File>Open Project. If the project’s version is older than the current engine version, you’ll be prompted to confirm regarding the update and offered to make an automatic copy.
When you launch an outdated project and no matching editor version are detected, you’ll also get the confirmation prompt.