Just wanted to add that jconn3 version is end of life and has been for some time :
End of Life Notice for ADO.NET 1.x and jConnect 6.x End of Life Notice: - Sybase Inc
jConnect 6.X November 30, 2011 (Jconn3.jar)
There are various issues in JConnect 6 that can cause errors or wrong data in ASE (and regardless of the version of ASE). So, if they don't currently affect 15.0.3, you will probably be OK against 15.7. But as Dawn states, any issues and you will be asked to upgrade to a current and supported version.