As far as the processing time and consumed memory is concerned, the complexity of the report layout, the complexity of the data calculations (aggregates, conditional formatting), the rendering media, the size of the generated document (in pages), and the capabilities of the underlying machine are crucial.
We would appreciate your thorough explanation of your scenario and a runnable sample project so we can give appropriate advise. That is why we would appreciate if you send us a sample application that we can run on our end and observe the problems you've elaborated on. Once we review it, we would be able to provide you with more info.
@Janusz - how many rows of data do you have and do you render them directly in the report or you use Table/CrossTab item?
All the best,
the Telerik team
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