When you want to do broad company-wide layoffs, you have to adopt some broad strategies, otherwise it'll be way too much work to find 15% of the company. It's like trying to do surgery with a scalpel when you really need a saw to amputate an arm.
Imagine the mechanics if they involved every single low-level manager in decision making. You'd never find 15%. Everyone would justify where a person on their team or their team as a whole deserves to be saved. So you apply broader rules (eg certain products, certain types of jobs, performance based). The upside is that you can avoid people-specific favoritism. The downside is that you lose good people in those areas as you're not distinguishing good from bad.
My current company did a layoff, not quite 15%, but in that ballpark. They went down as far as the directors and gave them a number. I.e. pick X people to lose. This was in addition to some specific cuts where they axed the entire product and all teams associated with it.
It definitely allowed management to cut a few people that had been on their short list for a while.
Imagine the mechanics if they involved every single low-level manager in decision making. You'd never find 15%. Everyone would justify where a person on their team or their team as a whole deserves to be saved. So you apply broader rules (eg certain products, certain types of jobs, performance based). The upside is that you can avoid people-specific favoritism. The downside is that you lose good people in those areas as you're not distinguishing good from bad.