I'm guessing that the part that takes so long to load is when the engine loads your level. If it takes a long time to compile your scripts the only thing you could try is removing unnecessary code like commented out code. When you publish your game, use the "compile to exe" option and this won't be a problem.

If the long load time is from loading the level, check how much RAM is used once the level loads. If there is a lot of RAM used you may have to reduce the size of your map that is loaded at once. You can still load other parts of the map when you approach a transition area.

If you find that only a little bit of RAM is used by your game then the storage containing the game files may have a slow transfer rate, possibly a slow networked drive. The last thing I can think of is it could be a script that is run on startup that is taking a long time to execute. Check if there is any complex code that would extend the startup time.