Let me share my experience with you first
It started with spending lots of time just setting up the open hubs,process chains and source system.Once the connection was setup properly, the next problem arose on extracting data from SAP BW, for some jobs it was fast enough but for others they just kept running even though the process chain at the SAP end had completed in seconds!
The worst nightmare was when the jobs were deployed in production and the jobs completed successfully - but they didn't extract any records (0 records were extracted) even though SAP process chain logs said that they fed many records! This was seen on not on single job but on 5-8 jobs!
Apparently, PMR was raised with IBM and they suggested to use 3 environment variables in each job to rectify the issue.
I don't exactly remember the variable names , but they were something like :-
APT_PROCESS_CHAIN_TIMEOUT
APT_OPEN_HUB_TIMEOUT
In your case, you can check with IBM if there are any environment variables available to speed up the process of data extraction.
Cheers!