Hi Suharsh,
Please take a look at SAP Fiori - Performance and identify the bottleneck. If the bottleneck is ERP backend side, most probably you have not implemented mandatory notes for SAP Business Workflow performance.
You can also extend the app and minimize the number of workitems in My inbox to 30 instead of 200.
You can also use Approve Purchase Order app instead of My Inbox. Approvers prefer to have separate tiles because number of workitems is on tile by task like Leave approval 5, PO approval 30.
Regards,
Masa / SAP Technology RIG