B737 FLT CREW BECOMES DISORIENTED AND TAXIES TO WRONG RWY AT IAH.

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CONTACTED IAH GND CTL FOR TAXI TO DEP RWY. WAS TOLD TO TAXI TO RWY 15L; HOLD SHORT OF TXWY E2 FOR INBOUND TFC. ONCE TAXIING; AS FO; I BEGAN TO LOAD FMC/CONFIGURE ACFT FOR TKOF. I TOOK A MOMENT TO CONFIRM HOLD FOR INBOUND AT TXWY E2; THEN RESUMED LOADING FMC. AFTER TFC CLRED TXWY E2; CAPT ASKED; 'ATC WANTS US TO GO OVER THERE; RIGHT?' INDICATING TXWY PARALLEL TO OUR OWN. WITHOUT CONSULTING THE ARPT DIAGRAM CAREFULLY; I REPLIED 'YES.' TAXIING RESUMED WHILE I READ CHKLIST; AND WHEN COMPLETED; I NOTICED WE WERE IN A LOCATION UNFAMILIAR TO ME. TWR THEN CALLED; ADVISED US WE WERE ENRTE TO RWY 15R; NOT RWY 15L; BUT TO TAXI INTO POS AND HOLD ON RWY 15R. WE COMPLIED; FLEW NORMAL TKOF AND DEP. NO FURTHER COMMENTS FROM ATC WERE MADE REGARDING TAXI. I FEEL I RESPONDED TO THE QUESTION FROM THE CAPT HASTILY AND IN THE WAY HE INDICATED; DUE TO HIGH WORKLOAD. IN THE FUTURE; I WILL REPLY MORE CAREFULLY AFTER A CAREFUL REVIEW OF THE ARPT DIAGRAM. INCIDENTALLY; THERE WAS NO INCURSION OF RWY 15L INVOLVED.