Hi @sushmajk
Is your issue related to using the Target UI or querying the activities via API?
My recommendation (based on past experience) would be to ensure any old activities are in either the "archived" or "ended" (if scheduled) state - this should be sufficient.
The default filters within Target Workspaces omit these 2 status types, however I generally avoid actually deleting old activities in case I need to refer back to them for some reason in future.
As far as I'm aware there shouldn't be any performance issues with a large list of past activities other than having issues finding old tests..
Also, QA links also stop working for activities in the "archived" or "ended" state.
https://experienceleaguecommunities.adobe.com/t5/adobe-target-questions/how-do-i-qa-an-archived-acti...
Thanks,
Jacob