Servoy JasperReports Plugin

I have one foundset based report which uses lots of calculations and stored calculation and the report runs too slow. And I also have few SQL based report which are as complex as the report I am having the issue, but they runs very fast.
Is there any way we can make the foundset based report as fast as SQL based report??

Few of my investigations:
1. The SQL based report consumes equal time for multiple run attempts. But for foundset based report it runs slow for the first time after I logged into the application, but with succeeding attempts it runs faster than the SQL based report. Not sure may be servoy is caching the foundset.
2. I have tried with Query builder, but there was not much difference.
3. I have tried to run the report with dataset instead of foundset, And I found out that the process consumes maximum time in filling the dataset. Once the dataset is filled the report runs very fast.