The XJR-15 was a Jaguar like no other road-car ever made by Jaguar. It was closer to the LeMans winning XJR-9 model, which took the crown at the famous endurance race in 1990 and in 1992.
The car was not designed by Jaguar. It was the creation of Peter Stevens, the man who designed the McLaren F1 later in his career. The XJR-15 featured a mid-engine architecture and no soundproofing at all. That helped the car achieve a very low overall weight of under 1100 kg (2336 lbs). The car was created by Tom Walkinshaw Racing. They said that they started with the racing vehicle, made the cabin wider and taller to accommodate two adult-sized passengers. Only 53 units were made.
The flatform with a bulb-like greenhouse on top was typical for a race-car from its era. There were two versions made: one for the road and one for racing. The road-going version, which was able to be registered, featured the turn signals and wider rear-view mirrors.
Inside, the cockpit featured two race-bucket seats and a dashboard filled with race-type switches and more gauges for speed, temperature, oil pressure, tachometer, etc. It didn't feature any radio, but it did have an intercom system with two headphones for the occupants.
The engine was a 6.0-liter Jaguar V12 unit, jointly manufactured by JaguarSport, a company jointly created by TWR and Jaguar. The British brand was never actually involved in the production. At least, not officially.