Hi,
From current description, I would suggest to use less subreports in one master report. Generally too many subreport would slow the report rendering. You could try in the master report build in more dataset and tablix area.
Also are you worry about the SP or SQL Server performance, for this aspect , you need to optimize the query in the SPs.
You could check Executionlog3 to know if the SP sql query is too slow or the report rendering is too slow.
Read though this article would help for the optimization direction : SSRS Reports Performance
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