Hi Clint
Tricky one!
There were as far as I can locate only three presentation groups which both reached 15 and used RE.8, Baroda (India), Gold Coast and Zanzibar.
Since we have one single word only Baroda and Zanzibar are applicable
Next problem is that the presentation was re-used on more than one aircraft
Baroda No 15: A3704, C2252 and C2986
Zanzibar No 15: B5012, F1586
Final problem is that I cannot locate any of them with No 5Sq.
However photo was taken in Sep 1918 which means most likely a late production aircraft is the one we are looking for which gives us two choices
1) Baroda No 15 C2986 which is only listed as with 1 AAP (whatever that was)
2) Zanzibar No 15 F1586 no unit.
Since F1586 seems to have been built late 1918 and no record of it until 1.1.1919 my guess (mind you guess
) would thus be C2986
Cheers
Stig