Hello guys, I have already solved the problem myself.
When I register normally, I've always had max. Download-Speed of 100kb / sec but i have normaly 6-7Mb/sec !

Now i tested with Proxyserver via NordVPN and a USA-Server i got 3,5MB / sek! Why is that ?

Nobody have idea why ?

By using a VPN, you're using a different network path that is skipping a (bad/slow) link.

Cheers!

 

Is this a porblem from the AVSIM servers to my Provider ? 
Or only my provider? Because otherwise I have no problems with download speeds? 
If so, can I bypass it without having to use a VPN?

We do not allow Proxy Servers or VPN ISP's and, when found, we will make the member's account inactive until the issue is resolved.  VPN's and Proxy Server's are used to hide a member's real IP address.  VPN's and proxies are almost impossible to detect but we have been very successful in finding those who are using one of them as we have tools found around the Internet to help us.

See also - https://whatismyipaddress.com/proxy-server

https://www.howtogeek.com/133680/htg-explains-what-is-a-vpn/

Luke is correct as you could be bypassing networks coming to the USA that have heavy traffic.

How did you determine how fast your connection was when connecting to AVSIM (when connecting first through your ISP, then through a Proxy, and then through a VPN)?  The speed tests are for connections to the Internet and not to AVSIM.  For instance, my Internet speed test shows I'm getting 102mbps but that was only with the person who owns the speed tests.  He downloads and uploads data from HIS servers through my ISP.  He said I had a very fast connection.  That's all you need to be concerned about.  AVSIM will be fast or slow depending on the number of guests and members on the site.  Sometimes we have over 1300 on the site at once.  If 500 of them are searching AVSIM for my topics and posts, that could bring AVSIM down to a crawl as searches take up a lot of resources. 

No one has faster Internet access to AVSIM because one is using a proxy server or VPN.  Access to AVSIM does not discriminate because of the ISP or type of service a member may be using.  There is an issue the OP needs to investigate if that is not the case.  Sometimes these Internet Speed Tests will provide recommendations to speed up your access.  Yes, like other websites on the Internet, AVSIM has its occasional bugs where access is slower than normal and we hear that from everyone when that happens!!  There are a lot of reasons why a site is slow.  AVSIM is not in the business of answering questions about download speeds or whether it is your provider or something else that is slowing down your access.  AVSIM is in the business of provide a website for flight simmer use.  Many are using your ISP, t-online.de and you are the only one so far who has complained.  Right now I can tell you are using a proxy or VPN as the location of your IP address is here in the USA.  For most, this is how one hides themselves from Admins/Moderators like me.  I recommend you use your IP address through your ISP soon. 😠