Crystal Reports XI - Oracle 11 - How to improve Performance?

Hello Experts....

Env: Oracle 11 and Crystal Reports XI

I have a requirement where i retrieve all customers with specific open contracts and then depending on type of customer i will go check their activity depending on the contract information calling sub reports.

So my main report is retrieving all open contract customers - which is simple and fine. than i have two sub reports to call deepening on kind of customer to check the customer activity, this by itself is not too bad in performance it takes a minute but by the time i run for all customer it is taking few hours.

i have changed my subreport data retreival from tables with report selection criteria to command object and passing customer and data range parameters to filter the data Not sure what else i could do? any suggestions on what i could look for is appreciated.

Thank you,