Slow query performance of simple SELECT query (Postgresql 9.6)
I could imagine an index on links_link (submitter_id, id DESC) being of great help here.

CREATE INDEX CONCURRENTLY link_id_submitter_id
                          ON links_link (submitter_id, id DESC);


It can be traversed to quickly find the subtree for submitter_id = 811645. Then the first node can be picked instantly to get the first record ordered by id DESC.