It is not possible to directly use or downgrade databases from newer to older versions.
You could try one of the import/export formats, as you mentioned.
- JSON-LD will probably not work for versions older than 1.5 (I'm not sure if it was already in the 1.4 version), also you might run into problems, because the schema has changed since then and there were some bugs fixed later on.
- ILCD and EcoSpold format were more stable already when openLCA 1.4 was released, so I guess this should be better suited. Just give it a try. You might loose some meta data though, so you should validate the import in openLCA 1.4 thoroughly