Some Possible checks to do if you have any Performance issues

If some one says that some application/process is taking 1-2 days to complete.

I would check:
if that server VM or physical, CPU, memory, DISK ,Tempdb, other databases related checks and

>I/O bottlenecks
>N/W bottlenecks
>Missing, unused indexes, Bad or duplicate indexes
>Stored Procedures count and see if we can tune the SP which is running frequently and taking more time
>READ/Write STATS
>TOP WAIT STATS