Nitro content is lowered from 15% to 10% by increasing the percent of methanol. Let's say you have two fuels, both with 20% oil. The label for one will say it has 15% nitro so that one has 15% nitro plus 20% oil leaving 65% for the remainder which is the methanol. The label for the other will say it has 10% nitro so it has 10% nitro plus 20% oil leaving 70% methanol. "Nitro" fuel is a bad name for it because it's more properly a methanol fuel. Nitro is just an additive to the base fuel and any engine will run just fine without any nitro in the fuel. I haven't used nitro in over 50 years. Well, once in a racing competition.