Live connections are usually slower.What i suggest is the following:
- performance recording:
enable performance recording on tableau server and see where it is taking time.identify bottlenecks in workbook.
- recheck how you are connecting in tableau and getting data
use tdc file
- use extracts instead of live connection
- did you check network latency and pingtime
- try applying DB filters to reduce the amount of data
- use explain plan to check the query stats
did you explore initial sql option ? few workarounds can be done in initial sql option.
hope it helps.