Large load records read using Salesforce Bulk API causing performance issues

We are getting records count ranging from 1-3 Million with SFDC Bulk API pull in less than 5mins but seeing delay in pushing the records to target (Rest Post).
The delay causing the performance throughput for the records processing to 10-15docs/second to target and hence the total time taken in SL is very large and also consuming large memory.

Pool size is 10 and also trying to apply parallelism by router snap calling 2 pipeline execute with same child pipeline.

Any other approach ? Can the batch size in REST snap help us here with pushing records in batches ?