updating a large table will always be slow. A good technique is to separate the inserts and updates into separate batches rather than mix them all up together.

If thats too much, indexing your update key columns will help. When talend is configured for "update or insert" It will issue a SELECT COUNT(*) query with the update key (advanced settings->field options) columns as the where clause. if it gets count > 0 it will issue an update; if zero an insert.