Postgres query to extract a JSON sub-object from a JSON field
I'd recommend (if it isn't already) converting to the type from json to jsonb and adding a GIN index. The documentation below lays it out pretty clear. Good luck!
 https://www.postgresql.org/docs/9.4/datatype-json.html

For my recommendation, reason for using jsonb as opposed to vanilla json is that regular json is stored as an exact copy in postgres and you cannot add an index to that column. Whereas jsonb has a smaller footprint and allows for indexing the specific column. I'd prefer to store it in a format that could be indexed to allow for queries to be more performant.