Horse 1426 - 15 Items or FEWER

I don't really mind if people verb a noun or noun a verb. I don't even mind if people adjectivise nouns or verbs. People have been tabling meetings, hammering nails and going for a walk for quite some time now; I have no problems for instance if something is described as chocolatey, but the thing that really sticks in my craw, gets my hackles up and my blood curdling, is when people and companies who should know better, do not, or if they do, perpetuate wrongness.
Of course you and I and everyone knows exactly what is meant by "15 items or less" but because this is a matter of pedantics and because I have a vested interest in this sort of thing, having bothered to learn grammar and thus have time and effort invested in the subject, then it makes the perfect subject for one of these little discourses.

"Less" and "lesser" should be properly applied to uncountable things. You can talk about less noise, less salt, less fuel etc. because although these things can be measured in discrete units, like decibels, grams and litres, it makes little to talk of them as countable things. As soon as you talk about 'some' noises, you immediately imply that there are different noises, but if it is just 'some noise' (in the singular, ie as an uncountable concept), there can be more or less of the generic thing we call noise going on.
I should also point out that when we say that 14 is less than 15, we refer to the uncountable concept of number, even though we do count it off; usually in discrete units of integers*.

"Fewer" on the other hand, refers to things which are countable - There are 9 boxes, 23 children, 6 pies. Each unit whilst they might be unique, have been counted as individual items which are assumed to be of the same class of thing; in this case, boxes, children and pies.
Most properly there are 5 fewer pies than there were yesterday, not 5 less. There were 4 fewer children in class today. There were 3 fewer boxes last week. These things are countable and counted.

So when I see a "15 items or less" in the supermarket, I cringe just a little. I know that all items for sale in the supermarket are countable because things are packaged as discrete items. Even when you order more or less luncheon meat from the deli, they still give it to you wrapped up as a single item to take it through the checkout counter, which immediately turns some luncheon meat into a single item which is countable. Unless of course you happen to be in an older sort of general store, in which case more or less flour might be perfectly acceptable but not discretely countable.

*Bonus Section - Warning Maths Ahead

I'm even wondering about whether the concept of more or less or lesser or greater even makes any sense in the realm of imaginary numbers. Is a complex number like 5i + 8 greater or lesser than 8i + 5? Is 5i less imaginary than 8i? Is -1 more imaginary than i because i² is defined as -1?