The real question here isn't whether SCAN can stop evaluating, it can, and the user's formula proves that. The real question is whether SCAN should be used for this at all. And the honest answer is no, not in the way most people expect. SCAN is built to carry an accumulator through every row of an array, outputting a value for each step. That's its job. Asking it to produce a shorter result, or to leave trailing cells blank, asks it to behave like something it isn't. The user's frustration is understandable, but the tool isn't the problem, the expectation is.
What the user wants is a running sum that freezes once it hits 15, with subsequent cells showing nothing. That's a conditional output, not a conditional calculation. SCAN handles the calculation perfectly: once `acc` reaches 15, it stops adding. But it still has to return something for every row, and the formula the user wrote returns the same `acc` value each time. That's why column B repeats 15. Column C, with its empty cells, is a visual preference that SCAN cannot deliver on its own. The function is not designed to suppress outputs mid-array. It's a workhorse, not a display tool.
So what should you do instead? Pair SCAN with a conditional formatting rule or a helper column that blanks out values after the target is met. Or use a combination of INDEX and MATCH to find the row where the sum crosses 15 and return only that result. The real insight here is that SCAN is a powerful building block, not a finished solution. It gives you the raw accumulation; you need to layer on the presentation logic yourself. That's not a limitation, it's the nature of working with array functions in a spreadsheet environment. They compute. You format.
This user is asking a sharp question, and it's the kind of thinking that leads to a deeper grasp of how modern spreadsheets work. The mistake would be to assume SCAN is broken or incomplete. It isn't. It's doing exactly what it was designed to do. The next step is to accept that and build the rest of the logic around it. That's where the real mastery begins.