I have something comparable here to look at.
I don't remember the history but it looks like it was originally built for a Fora .049.
At some point it had a .15 engine mount grafted onto it.
I DO recall using a OS.15, 6.5 x 5, bladder, big venturi and open exhaust.
As it sits here ARF with a 270 NICAD, a pair of servos and just needing an engine and a RX it weighs 15 ozs.
If you add a stripped down .15..what's that, another 6 ozs or so...?
So, 22 inches of span, 18 inches long, possibly 22 ozs RTF and it ended up being a decent flyer after a few failed launches. It was twitchy in roll to the point of just needing 1/16" of aileron either side of zero. Pitch control and glide were OK, but yes it did resemble car keys . I even had the onboard pitot tube speed sensor in this thing and seem to remember 130 mph from the CVA, but I won't swear to that..
Is going this small and heavy worth trying...? It is if you are a little bit adventurous and don't care too much about the outcome
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26 inches of span would make setting it up less critical and it would still be plenty fast.