Oracle Database Discussions

Hello There;
Our company OLAP database is facing performance issues where 1 simple query could take it more than to 20 mins to return result.

I am newbie to Oracle DB, i was told to look at the explain plan and yes , the plan looks alright where it uses all the indexes and there is not any full table scan. Now i suspect it is due to the SGA, PGA and BLOCK SIZE setup.

Can anyone give me a clue on how I can size the right SGA, PGA and BLOCK SIZE? The server has 16GB memory, 64bit, running only the Oracle 9i, and here is an extract from the INI file. Any advise would be very much appreciated.

*.audit_trail='DB'
*.background_dump_dest='/opt/app/oracle/admin/PRODOLAP0/bdump'
*.compatible='9.2.0'
*.control_files='/export/oradata/PRODOLAP/ctrl/control01.ctl','/export/oradata/PRODOLAP/ctrl/control02.ctl','/export/oradata/PRODOLAP/ctrl/control03.ctl'
*.core_dump_dest='/opt/app/oracle/admin/PRODOLAP0/cdump'
*.db_16k_cache_size=3154116608
*.db_block_size=8192
*.db_cache_size=1577058304
*.db_file_multiblock_read_count=32
*.db_files=400
*.db_name='PRODOLAP'
*.dml_locks=200
*.global_names=TRUE
*.instance_name='PRODOLAP'
*.java_pool_size=20971520
*.job_queue_processes=0
*.large_pool_size=150000000
*.log_buffer=524288
*.log_checkpoint_interval=10000
*.log_checkpoint_timeout=1800
*.max_dump_file_size='10240'
*.max_enabled_roles=30
*.open_cursors=800
*.open_links=4
*.optimizer_index_cost_adj=50
*.oracle_trace_collection_name=''
*.parallel_max_servers=5
*.pga_aggregate_target=1572864000
*.plsql_v2_compatibility=FALSE
*.processes=500
*.remote_login_passwordfile='NONE'
*.resource_limit=TRUE
*.rollback_segments='RBS01','RBS02','RBS03','RBS04','RBS05','RBS06','RBS07','RBS08','RBS09','RBS10'
*.service_names='PRODOLAP'
*.session_cached_cursors=100
*.sga_max_size=5242880000
*.shared_pool_size=209715200
*.sort_area_retained_size=6553600
*.sort_area_size=10485760
*.sql92_security=TRUE
*.user_dump_dest='/opt/app/oracle/admin/PRODOLAP0/udump'