In Japan, maximum nitro allowed is 20% or 22.5% and no more so YS engines are perfectly happy with this. I personally have run every YS engine from the 61 2 strokes to all the 120 variants and all the 140s except the DZ with coolpwer 15% with no problems whatsoever despite very high humidity where I live. I have only run the 140DZ and 160DZ on 20% and 30% nitro but see no reason why 15% nitro wont work. Properly tuning the engine is the key. Tried using 10% nitro on the YS and coulnt get it to run like I wanted so I would say that either I am not a good enough engine tuner to make YS engines run at 10% nitro or YS engines wont run right at less than 15% nitro.