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This simple recipe shows you how easily we can now use SSDT for Visual Studio 2015 with prior SSIS versions. If you open an existing SSIS project that is developed in the SQL Server 2012 or 2014 SSDT version, the designer (SSDT) will be smart enough to select the right target version (2012 or 2014) without upgrading your project or packages.

The default Target Server version is SQL Server 2016. If you created your SSIS project without setting this property and try to deploy it on a prior version to 2016, the deployment will fail. Also, if you change this property from, for example, SQL Server 2016 down to SQL Server 2014 and your package uses new SSIS functionality, the project won't build and therefore you will not be able to deploy it.