Model : TL-WR841N

Hardware Version : V9

Firmware Version : 3.15.9 Build 140530 Rel.37695n

ISP : cable, modem Cisco

Hello
I have 15Mb down internet, when i connect my pc directly to my modem everything is ok, but through TL-WR841N my down speed is ~100KB/s, ping is ok.
I am connecting with cable and for testing i connect only 1 pc and turn wifi off.
Also when i connect my other (old) router it works like it should.
I tried factory seatings, no QoS, UPnP, firewall on and off, no mac filtering, speed is slow over cable and wifi.
Pls help

[Mod pls remove the two mirror threads, sorry for the trouble]

Thank you