The body has to be completely scratchbuilt, so are the wheels.  However, the part of the interior, engine and suspension details can be built by using a Tamiya's XJR9 LM kit.  The tires are Bridgestone Expedia, and the Tamiya's XJ220 kit contains this brand.  The size isn't quite the same, but it is usable.

There are three types of XJR-15, the race, street and LM version, and I intend to make all three of them by duplicating the parts.  The difference between the race and street version is minimum, but the LM version features an extended front airdam, air inlet on the roof, and repositioned rear wing.  The 7.4 litter engine of the LM, which appears to be the same except the inlet, is supposed to produce 760hp! compared to 450 hp of the 6.0 litter V12, available in the standard  model.