Are you sure? Small blocks run hotter plugs then big blocks! Most if not all small blocks run a medium to hot plug and big blocks run medium to cold plugs. Now a lot has to do with what percentage of the fuel you are running. I would think the T 15 came with a HPI R3.

I guess some did not read the link I posted so here is a cut and paste from it.

Size matters to glow plugs. What size is your engine? A .12? .15? .21? Big engines have more mass and retain heat better. Smaller, lighter engines don't, and need the help a hotter plug can offer.