My server wont let me upgrade to 1.15.2

Hi, I recently started using Aternos a month ago when a friend suggested it to me, I decided to set up an account and run my own server. It was called LokiSurvivalWorld, and of course, it was made in 1.51.1, it was running just fine for awhile, I set it to forced survival and allowed my friends to use cracked version because they can't afford to get the vanilla game.
However, when I went to load my server, My mc updated to 1.15.2 and now won't let me onto my server, saying it's outdated. I've turned on force upgrade and restarted it, hoping that worked, nothing. My next idea was to download the server world and load it as a single player world, as it originally was one and I was hoping my MC would force to update to .2, but when I moved it to .minecraft > saves, it won't show the world in my world menu. When I downloaded it, it was known as BreathOfTheWoof-world2.zip, I of course, extracted it. I figured the hyphen in the name was part of the issue, so I renamed it to BreathOfTheWoofWorld2, but the folder still refuses to show in world menu, even after I restarted my mc and made sure it was the latest version. My friends said to just use a 1.15.1 snapshot, but i don't know how to do this and I'm pretty sure that's only temporary solution. Anyone got any suggestions on what to do?

Ok, I found out what was wrong, turns out you can install 1.15.2 drivers through Aternos, i found while twittling with change version settings, thanks for the help anyway!