I have below string which returns different results in version 14 and 15. Version 14 gives correct results but version 15 is off by 5 hours.
SELECT CAST(CAST(CURRENT_TIMESTAMP AS CHAR(19)) ||'-01:00' AS TIMESTAMP) ;
Result: 2016-02-26 14:38:56.000000
Result: 2016-02-26 09:41:12.000000
Your session time zone offset is different (look at HELP SESSION), likely due to differences in how dbscontrol and/or tdlocaledef were configured.