Error when joining the server

Hello.

I created a 1.14.4 aternos server in november 2019. Yesterday I decided to update it to version 1.15.2. I opened the server, and when I wanted to join I got this error: https://prnt.sc/r9hrwo

I get it when joining with any version above 1.15. If I try to join with 1.14.4 again it says that the version is outdated.

If I try to change the aternos version back to 1.14.4, it tells me that my world will be deleted and I will lose all my plugins and progress.

What can I do?
Thanks.

https://mclo.gs/2A0x2zN

What does that mean? In singleplayer?

I did what you said.

Now I can join.

But of course, none of my plugins are working.

https://mclo.gs/Q1r2k5C

This is the new server logs, if you want to see it.

But I can't just remove the plugins!

That would remove all players' homes, it would ruin the economy, the shop wouldn't work anymore, all the locked containers and private stuff would now be unlocked. I worked months on all this. Is there any other way other than removing the plugins? What if this is not the solution?

I solved the problem. Thank you very much my friends!