Performance Tuning :: OWB Mapping - Cube Load

I have a OWB mapping which takes input from a staging table and add those row to the Cube. The underlying table behind cube is a relational fact table joined with the dimensions using foreign keys. Explain plan behind the query has a rather high cost and the mapping runs for 30 minutes. If you see below, in step 17, the cost goes up to 1,396,573 which is also where nested loops start to appear. Query plan is also attached in the image format.

Plan
SELECT STATEMENT ALL_ROWSCost: 1,746,526,275 Bytes: 386,835,904 Cardinality: 464,947
46 NESTED LOOPS OUTER Cost: 1,746,526,275 Bytes: 386,835,904 Cardinality: 464,947
41 NESTED LOOPS OUTER Cost: 1,744,200,663 Bytes: 380,791,593 Cardinality: 464,947
37 NESTED LOOPS OUTER Cost: 1,743,270,415 Bytes: 374,747,282 Cardinality: 464,947
34 NESTED LOOPS OUTER Cost: 1,740,476,128 Bytes: 368,702,971 Cardinality: 464,947
29 NESTED LOOPS OUTER Cost: 1,739,545,862 Bytes: 362,658,660 Cardinality: 464,947
25 NESTED LOOPS OUTER Cost: 1,710,193,475 Bytes: 356,614,349 Cardinality: 464,947
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