lemmy updates did some improvements on the receiving side, parallel sending on the sending side is not yet part of a new release. it'll also likely take some time for that to be deployed on lemmy.world to have those changes be tested by other production instances first. my activitypub-federation-queue-batcher is currently used by at least 2 other high latency instances and would address the issue at the cost of a small (like 3 bucks or so) vps in Europe and some time investment for the setup.