This is really all about cadence. You break up a text, at various levels, as an expression of its cadence. A slower cadence tends to express itself in longer sentences, longer paragraphs, longer chapters. A faster cadence tends to express itself in shorter sentences, shorter paragraphs, shorter chapters. (I say "tends" because I don't think these are iron rules by any means.)
Different styles and different genres tend towards different cadences. (That word "tend" again.) Thrillers and crime stories tend towards fast cadence, epic adventures and literary works tend toward slower cadences. There is no inherently right or wrong cadence, just the cadence that is right for the work.
The cadence of a work can also change over the course of the story. Sometimes the cadence will pick up towards the climax, for instance. Other works proceed at an even cadence.
Cadence is not the same thing as the pace of the action, it has more to do with the feel of the work. No Country for Old Men springs to mind as a work with a fast pace but a slow cadence.
Since your work exists already, its has a cadence. You simply need to fit your chapter breaks to the cadence of the existing piece.