Eclipse often performs a lot of background tasks with source code, so large projects can lead to reduced performance. To get the best performance, you should break work operations into smaller projects and have these projects be dependent on each other.
You can use the COBOL Copybook and Remote COBOL Copybook project types to create project that hold several copybook files. In these projects you can only create new or add existing .cpy and .cbl files but files with the .cbl extension are treated as copybooks.
You can then add these projects as dependent projects to the build path of other projects that include the source files. Copybook projects are not compiled, thus saving processing time and resources.