Can you check the link speed on your Mac to verify? G o to Network Utility, then hit the Return key to launch the app. go to Info to check link speed.The Mac will automatically connects to 2.4G wifi...

You login from pc or from your phone? The default password should be admin as well, no caps, all small letters.

Did you reset it? What's the original firmware version? Can you still see the tplink wifi on your phone?

Where do you see that the router supports TR-069? I couldn't find it on my router.

If the problem just began lately, maybe you can reset the router.

You've disabled WLAN, that will cut the power consumption a bit. I don't know other way to do it. You can do some tests.