C-15 is the fastest fuel of the three
C-15 is the best for N/A big bore engines and has only 10% aromatic hydrocarbons. The burn rate is faster than C-16 which works best in blown and turbo applications that require high detonation resistance. Now C-14 has no aromatic hydrocarbons which will make it difficult to read your plugs due to no soot indicators that most of us are used to seeing on the plug. The cost of these fuels are nearly the same and I have used all 3 in big bore N/A single carb engines. The C-15 is much faster in 4.60" bore engines than C-16 by a bunch due to the faster burn rate, and the SG of .713 keeps you from running huge jets that the C-14 will need with it's .690 SG.
C-14 needs to be tuned on the dyno with oxygen sensors to get the tune-up quickly, plug reading is challenging without aromatic's.
C-16 has 6 grams of lead compared to 4.23 that the 15 and 14 have and having 20% aromatic hydrocarbons make's the plugs dark when rich.
C-15 is clean burning, low in aromatics, high octane and fast burning. My first choice for your application C-15, C-14 would be my second choice.
I was once informed that C-15 is C-12 and C-14 mixed 50/50. The behavior of 15 is similar to both 12 and 14. For what that might be worth?
Bruce