Oracle SQL Query Slow IO Slave Wait

Hi,

Recently the below query taking long to execute.

As per check, it wait for io slave wait event.

Can i get some advise on how to fine tune this query.

SELECT b.*,        Round(fwrpt.utl_cal.DELTA(start_assy, received_assy), 2)     ASSY_CT,        Round(fwrpt.utl_cal.DELTA(ordercreationtime, invoice_date), 2) DTD_CT FROM   (SELECT a.shipment_year,                a.shipment_per,                a.shipment_ww,                a.customercode,                a.customerlotnumber,                a.device,                a.PACKAGE,                a.leadcount,                a.shippedqty,                a.actualshipmentdate,                a.lottype,                a.alias,                a.received_assy,                a.start_assy,                ASSY1 COMPLETION_ASSY,                ordercreationtime,                invoice_date         FROM   (SELECT shipment_year,                        shipment_per,                        shipment_ww,                        customercode,                        customerlotnumber,                        device,                        PACKAGE,                        leadcount,                        shippedqty,                        actualshipmentdate,                        lottype,                        alias,                        diesreceiptdate                    RECEIVED_ASSY,                        timedstoasy                        START_ASSY,                        ordercreationtime,                        invoice_date,                       (SELECT Max(txntimestamp)                         FROM   fwwiptransaction b                         WHERE  b.wipid IN (SELECT sublotid                                            FROM   fwrpt.t_sublot_cyctm d