true about incenery rounds. regarding the leader speed on recon, it takes time to make sketches of enemy positions in that shakey crate. and you can't see enemy if you just buzz around full speed.
not sure if they had photo equipment in 1915 already, but that, i guess, would need really slow overflights as photo equipment worked only on longer exposures and you cant do that flying fast. it had to be slow steady flight or phots wouldn't show much.
however, it is all guessing