You can turn 15/15 into 10/10 by adding methonal to the 15/15.

For instance take 9 ounces of 15/15 and add 3 ounces of methonal will make 12 ounces of 10/10.
Then add that 12 ounces to 24 ounces of gas and you will have 36 ounces of gas/glow fuel

Or take 3 quarts of 15/15 and add 1 quart of methanol and you will have 1 gallon of 10/10.

It's 2 am but I believe this is right, if not someone out there will catch a mistake.