You never know. Generally though I would think it would missfire from being far retarded. That depends on the chamber piston etc. I can't say I have ever seen an " Naturally Aspirated" engine like 15* total but there is a first for everything.
On my old sbc we used to leave the line with +1 at times on a .042 with no progressive.The bbc has 2 big stages and timing gets pulled back to 1 or 2 btc twice in the run,once on the 1st and again when the big ass 2nd turns on.
Make sure the rotor phase is spot on or it will give you a bang out the carb.I run 30* initial, 16* going down track , phase rotor at 14* for a little extra room.
i have no idea what happened, beleive it or not the plugs looked OK defeinately rich but not what you would expect. #4 and #7 had the ground straps missing. I thought maybe it crossfired? or when it did finally fire it the coil stored so much energy it just melted the straps ...i dunno what happened. Figured id see if anyone else has done something similar.