The publication doesn't say whether the P15 will use some kind of electric assist. If it's as basic and light as implied, there's a decent chance it won't be electrified. But McLaren has previously said it wants to have electrification in all of its cars within 10 years, and that was back in 2014, plus the P1 and the upcoming BP23 had and will have hybrid powertrains. So it would seem natural to give this P15 some form of hybrid motivation.
There are reasons to believe this rumor. Back in 2014, McLaren did confirm to us a report, brought up by Autocar, that it was working on a car with the P15 designation. At the time, it was predicted that this car would fit between the top level Super Series car, which is now the 720S, and the P1, and cost roughly half a million dollars. That would at first seem to contradict this new rumor that the P15 will be quicker than P1, but perhaps McLaren will still position it lower if it's as bare bones and stripped out as Autocar suggests.
Additionally, Autocar was right about a rumor that McLaren was working on a three-seat F1 successor. which turned out to be the aforementioned BP23. McLaren's CEO confirmed the car's existence and three-seat layout along with a few other details. Specifically, it will be the fastest, most powerful McLaren yet, it will use a hybrid powertrain, and McLaren will build only 106 units. Not long after came an official sketch revealing a sleek, slippery profile.