Bug reports without an attached log file are usually useless.
Can you post a full session log file showing a file transfer, both in 5.15.9 and 5.16.5 RC?
Yesterday night I reinstalled 5.15.9 and everything is back to normal.
Re: WINSCP 5.16.5 RC overall speed slow
What version of WinSCP were you using before? If you downgrade, do you get the speed as before?
WINSCP 5.16.5 RC overall speed slow
I'm a long time user and never had any problems with WINSCP until today after I updated Windows 10 and WINSCP to 5.16.5 RC. Overall speed is too slow something I never experienced before. I tried the recommended fix at https://winscp.net/forum/viewtopic.php?t=25705 and upload/download speed improved but overall speed is really too slow as never I experienced before.