Check the ExecutionLog view on the ReportServer database. The view will give you information on duration spent on Data Retrieval, Processing, and Rendering.
Compare the logs from Prod vs Dev and see where the difference is for the specific report. If the processing is taking up a lot on Prod, verify that you don't have resource issues around CPU, RAM, and disk queue. Reportserver caches temporary data in ReportServerTempDB. This allows you to go through pages of reports and re-render the data without having to re-query the database. For reports that return lots of data, the bottleneck might in caching the data.