Basically the easiest way to optimize the performance in current case is to make the target field complex type (to contain the nested object directly) and not use the ForeignKey column. This way each record would contain it's text representation and remove the need of loading all items initially. Additionally you can make the editor for this field to support search and load only the top 10 records from the search result (server filtering). Please check the example below:
Another option is to filter the values for the ForeignKeyColumn only to the ones that are selected in the current records.
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