Peter Chinn "Latest Engine News",Model Aircraft (British) June 1962. discusses the Fox 15X  and 15XX.  These are later models which look sort of like a Stunt 35. The 15X on 20% nitro turned Tornado 8 x 4 at 11,600 RPM, The 15XX turned 12,800. I don't know about modern 15 glows, but Ron Warring, "Engine Analysis", Aeromodeller Jan. 1962 gives figures for the short-lived TD 15 of between 15,200 - 16,000 on 20% nitro.  A TD 09, way overpropped, on 30% nitro, will turn an 8 x 4 at 13,200.  A Medallion 09 is about the same as the two models Fox 15 with an 8 x 4.

Here is a link to copies of the engine reviews by Peter Chinn for the British mag Aero Modeler. The Fox 15X review from 1962 lists the weight as 3.6 oz- that would be without a muffler. The 1959 review of the older Fox .15 ( 2 bolt rear cover) lists the weight at 4 oz.

http://www.the.elmores.btinternet.co.uk/engine_tests/_cat001.html