I have written a function in postgreSQL which returns integer.
The function was taking only .05 seconds to execute in the DB.
The DB was then backed up, restored and upgraded to PG 15 from PG 10.
All the data, pg_setting parameters, indexes are all the same in both DBS.
But the same function call is now taking 0.5 seconds to load instead of 0.05 seconds.
Is there any solution?

I checked the indexes, reindexed, effective_cache increased, buffer increased, effective_io_concurrency increased and all other pg_setting parameters increased.
Vaccum analyze done.
Still no improvement.