The most wrong thing you have done is buying an engine based on the paper specs. Paper specs does not mean a thing......

If a .15 is the max you can get and you wanted to have the best performing engine I do not think a GO is the right choice. I know in the 235mm onroad scene the Novarossi and Picco .15 engines were the way to go and now even today's .12 racing mills are better than the populair .15 models from then.