As a report developer, it can be frustrating a report developer, knowing that something is slow, but not being able to put your finger on it. In my mind, there are 4 main areas where there might be a slowdown:
1. Data refresh
2. Model calculations
3. Visualization rendering
4. Everything else
Identifying which one of these is the problem is the first step to improving performance. In most cases, if a report is slow it’s an issue with step 2, your data model.
Eugene has plenty of good advice here.