SQL Server - Slow Database for no apparent reason
I don't know SQLServer specifics, but usually this sort of thing is due to table statistics being different in the two databases. Look at the query plans to see if they are different. Run the SQLServer version of "analyze table" or "analyze schema" commands.
If these things don't help, check how the databases are set up. Is it possible that the data is identical, but server configurations are different, and, for example, there is a much lower threshold on available memory for the production version.
As you said Indexes are not fragmented, Kindly check for the one with values above 30 % as FRAG value for pages greater than 1000.


You can proceed point 3 with Updating stats by running command: EXEC sp_updatestats; on database with slowness issue.