Performance issues can be caused due to several scenarios. First of all make it sure that what is making it worse in performance.
1. A slow dashboard Slow Dashboard or Workbook Performance | Tableau Software
2.optimize your server performance Optimizing Tableau Server Performance | Tableau Software Authoring for Performance on Tableau Server | Tableau Software
3. database query performance Improving Database Query Performance | Tableau Software
Finally go through this article it will give you a lot of insights Designing Efficient Workbooks | Tableau Software