Half way through reading your post I was thinking "you need more than 15% nitro", 30 is closer to the mark..most people will be using 20-30%.
Many people mix there own fuel and so long as it is mixed correctly with good ingredients then there is no reason your engine will expire early.
A member of this forum recently posted his method and ingredients he used in his own fuel.-
http://www.rcuniverse.com/forum/m_11253940/tm.htm