Follow the below steps
1. Delete all unwanted sheets
2. Hide all Unused fields in your data pane
3. Limit your data by adding a Datasource filter(If possible)
4. Also, you can try to create an Extract of your data if possible
5. Delete all unwanted calculated field.
6. Try to create all calculation field in the data pane and then use it in the view.
7. also do a performance recording to your workbook and figure out the worksheet where the elapsed time is too Long
These are some of the steps that might help you in resolving the issue. Try this and update your comments
If you have quite a few of those nested calculations (either within a calculated field or split into multiple fields) we always suggest pushing it to calculated at the data source level rather than in Tableau.
Also, if you have multiple worksheets in a dashboard, then it will take time for the view to load and render.