Lem, if the sys A failes the pressure will be locked by check valves in the sys ,locking also the spoilers.
In order to release the gear,(in case of ldg gr lever jammed up ) you'll cycle the speed brake lever,releasing the pressure.
This will leave the spoilers unlocked.
Jabbara gave you the right answer concerning the aerodinamics of using flap 15, I guess.
That phrase I ve underlined in my previous answer it's in the Dec 3,2004 revision of the QRH.
Brgds
Alex