First of all I want to apologize for my English, I hope you understand me correctly.
I have a database migrated from a SQL Server 2005 in a SQL Server 2014. Well, in addition, I have a .NET process that uses ODBC connectors to execute stored procedures in the database.
My problem is that this process lasts 20 minutes against SQL Server 2005, and against the migrated database in SQL Server 2014 it takes 8 hours. After many tests, if the level of compatibility of the database to SQL Server 2008, the process takes only 8 minutes.
Any idea of the reason? What problems can I have when lowering the compatibility level?