Please let me know whether ArcGIS 10.2.1 supports Oralce 12c R2
It doesn't seem so: Oracle database requirements for ArcGIS 10.2.x
Supported database versions
Standard/Standard One/Enterprise Editions:
Oracle 10g R2 (64-bit) 10.2.0.3
Oracle 11g R1 (64-bit) 11.1.0.7 (see note below)
Oracle 11g R2 (64-bit) 11.2.0.1 (see note below)
Oracle 11g R2 (64-bit) 11.2.0.3 (see note below)
Oracle 12c R1 (64-bit) 12.1.0.1 (see note below)
Also check this thread: ArcMap 10.2.2 Oracle 12c : Crash
Support for Oracle 12c R2 seems to have started from ArcGIS 10.5.x : Oracle database requirements for ArcGIS 10.5.x—System Requirements | ArcGIS Desktop