Realms struggling to run large/old worlds

My friends and I have a world we've been playing on together for over seven years now. We previously ran it on multiplayer servers but found them too unstable and laggy, so we switched over to realms and have been mostly satisfied with the experience. Recently though we've needed to save the world to single player to do some file modifications such as adding loot tables or modifying our nether, and Minecraft can barely handle it. The most recent time we tried this I timed it and the download and reupload process took about four and a half hours, with both transfer crashing multiple times. I'm worried very soon we will be unable to move the world anymore.