That 15% no longer has the majority of the economic power in the world, or anywhere near it. There's a great visualization of the G7 vs BRICS here. [1] That's obviously not all countries, but those omitted aren't going to change the result nor trend. Just as important is what "economy" means. When we speak of war we're referring to the ability to go from ploughshares to swords, but most of the 15% have neglected their core manufacturing competencies and transitioned to service economies where these large numbers don't really translate into economic might of the sort we might imagine. Again, yet another lesson from Ukraine.
[1] - https://www.statista.com/statistics/1412425/gdp-ppp-share-wo...