The McLaren M15 is one of the Mclaren entries the open record knows by name, and by little else. That is not nothing: a name in the catalogue is where a car's story starts to be recoverable. The shape is credited to Gordon Coppuck.
The background
The McLaren M15 was an open-wheel race car designed and built by the McLaren team for a single season of competition in 1970, and was their first attempt at making an Indy car. It was later replaced by the more successful McLaren M16, which went on to win three Indy 500s; in 1972, 1974 and 1976.
The engineering
the output is 650 hp. On the scales it comes to 1490 lb. That is roughly 436 horsepower per tonne: hypercar territory, where the limiting factor is the tyre, not the engine. The wheelbase is 99 in. These are manufacturer figures carried by Wikipedia and Wikidata, not road-test measurements.
Where it sits
In the Mclaren line-up the McLaren M15 has a clear place: it handed the line to the McLaren M16. Its Mclaren stablemates include the McLaren M16 and the McLaren MCL33.