First of all, their claims are not new. They claim this for a long time already but have not shown a minimal viable product yet. During the time they spend money in research, Tesla batteries grew to 3 times the originals.

QuantumScape have only shown minuscule batteries, they need to scale up to car battery capacity. Only a car with their battery can prove their claims. Until that happens their stories are worth nothing.

Charging a 75kWh large car battery in 15 minutes requires a charger of at least 300.000W. Imagine a charging station for 5 cars would need a 1.5MW power station. That is impractical. Also the current flowing into the car would be enormously high, requiring huge cables. Also inside the battery pack, huge cooling systems are required.

More practical solutions are exchanging battery packs or battery fluid exchange (flow battery). In short time 100% recharge and virtually unlimited range if packs are slowly charged at exchange hubs. .

QuantumScape will water down their claims and eventually publish a more or less standard LiFePo battery if the investors are lucky.