Gather stats slowness on partitioned table on DB 12.1.0.2

We have a common Oracle Home 12.1.0.2 for our Unit & QA database hosted on same database server where we are gathering stats on a partitioned (156 partitions) table manually using below command. The table has incremental stats enabled in both environment and there is an partitioned (156 partition) index PK_1894 on the table. The testing team is loading the data in exact same way in both the environments and we confirmed that they are not loading or updating data in older partitions.

dbms_stats.set_table_prefs('OIDFATM','FCT_COMMON_POLICY_SUMMARY','INCREMENTAL','TRUE');

dbms_stats.gather_table_stats(ownname=>'OIDFATM',tabname=>'FCT_COMMON_POLICY_SUMMARY',cascade=>TRUE,degree => DBMS_STATS.DEFAULT_DEGREE);