Highly variable - what aspect is slow - calculating a sheet, drawing a chart? What is your data source? Have you extracted your data if reading from Excel/text/etc.? Are you using table calculations that could be optimized? How many rows of data and how many sources? Are they joined/blended? What filters are you using?
Help us understand and I'll bet there's something we can help you with.
In order to "isolate" the driver for the performance issue, I would start by running a similar query to the one feeding into the Vis, using another tool (is your data source relational or multi-imensional?)
If you are using version 8, you can try the Performance Recorder:
- "Help" \ "Start..."
- Navigate your visualizations as usual
- "Help" \ "Stop..."
After stopping, a brand new dashboard will show up, with some basic statistics about time-consuming components.