Standard in the sense of one size being standard is a meaningless concept as applies to bicycles. There are multiple standards which exist at the same time.
9mm is the standard for front QR axles and fork ends, 5/16 or 8mm is another standard used for lower end bolt on wheels, and there's the 15mm thru-axle standard which is growing, but likely will stay for heavy use or DH mtn bikes.
In any case, a 15mm system calls for an entirely different fork, and will not work on one built for "standard" QR wheels.
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