[Arran]

I believe that you are correct, that the resistor is R15, though the parts list shows it as being a 12,000 ohm resistor not a 15,000 ohm one. It's used to supply the screen grids of the tubes in the front end, and seems to be the only one listed as more then 1/2 a Watt on the parts list. This doesn't mean that the original wasn't changed, the parts list specs it at 2 Watts and most wire wounds are higher then that, if C4 shorted or became very leaky it would burn up R15 if it was a carbon resistor. I think that the orange resistor must be R14, it's supposed to be 30,000 ohms, and the cap next to it is likely C4 as they are connected in parallel, it's very likely an RF bypass.
Regards
Arran