migrating a map from one project to another project

I would like to migrate a whole map from one project with all the content placed on it to another project.
Now here’s the problem. The mesh, terrain, BP, playerspawns and co. should be included too. However those files are not in the project I would like them to be.
Why not mirgating all from the first o the second project. Well thats way too many GB and when packeing it could cause major problems…

Any suggestions?
Thank you very much in advance!