Hi

It is expected, as Firebird do not have parallelism on single connection. Then the best results is with high power core rather then multiple cores. Multiple cores are used by multiple connections. And in this case FB3 is the winner, as it spread jobs better then FB2.5.

But in your case you should look more on that stored proc, as 15 minutes is long time. I have changed many sp into single query with cte, recursive cte or by using window or psql function in fb3

Regards,