Hello sorry to reopen this thread , but im having same problem as the thread creator , did all of those changes nothing

only download speed reduced by 3 times atleast while on router .
firmware : 8.03
router : dir 615-h1
I have same ISP as caspeer ( thread creator )
We can use teamviewer if possible , im out of solutions ( tried without wireless/firewall/ antivirus ) , no improvements
Thanks in advance <3