15% is from the 2011 WHO report on disability: https://www.who.int/teams/noncommunicable-diseases/sensory-f...

The more recent WHO's Global report on health equity suggests 16%, as populations age: https://www.who.int/publications/i/item/9789240063600

The CDC considers this closer to 30%: https://www.cdc.gov/disability-and-health/articles-documents...

This number is generally considered to be rising for a few reasons. Aging population, wars resulting in higher injuries but fewer deaths, the number of people who are able to survive disease (rather than historically just dying.

You might find the Washington Group's definition, which applies a spectrum, and estimates an approximately 6-12% rate of disability. https://www.washingtongroup-disability.com/wg-blog/post/diff...

> I doubt the number would get anywhere close to 15% if the definition only included the kinds of disabilities that are immediately obvious to anyone looking.

Thank god that's not the definition. Deafness/significant hearing impairment isn't immediately visible, and that's estimated at ~5%. Plenty of folks are low vision enough to need assistive technology (like a screenreader) even if they don't have a cane and may be able to navigate. Plenty of people with MS have great days where they can walk, and days where they cannot. There are people who lack the strength in their hands to dress themselves, yet they can go out and about just fine.

Your definition is too narrow. Plenty of people experience impassible barriers that are not visible. Happy to provide some additional educational resources for you if they would be helpful.

> Certainly it's not true that 15% of the people I see are in a wheelchair, on crutches, missing a limb, obviously blind (e.g. walking with a cane), and so on.

Are you in a wealthy area? Think globally, do you think your town has better or worse support than other parts of the world for people with disabilities? Do you think your region has better or worse regional conflicts or disease? Think globally.