iPhone 6+; iOS 9.1; TP Link TL841N router: Experiencing slow wifi since morning

Hello I m in India. my phone was working fine and I think was running 9.0.2. However in the morning i noticed the following issues.

• Wifi on my phone (iPhone 6 +) is extremely slow. Some sites open but some dont. Most times, nothing opens at all.
• Other devices like 2 macs, 2 ipads, and one iphone 5 run fine on the same wifi network.
• I use Whatsapp and they have a web based desktop client. But the client requires the phone and the mac to be on the same Wifi. So if for ex: the phones Wifi is off, the client on mac shows that it cannot connect to the phone (yellow pop-up). Now i have noticed that the iphone may be dropping the connection, since this pop up comes and goes.

Here are the things I have tried so far.

• Reset network settings.
• Rebooted phone, wifi, both
• toggled airport mode.
• turned of the wifi networking services under system service in privacy section of the settings.
• Updated to 9.1. Doesnt help.
• Interestingly, the 9.1 was downloaded OTA on the phone using the same wifi!
• Used Google Chrome browser. My subjective opinion is that it opens more sites but I could be wrong.

I have the following questions

• Why all of a sudden? If i could use it all night and all the months before that then why today.
• Is there any fix for this? I see that many people have reported the same problem many times over. I m surprised why this isnt being fixed.
• Is it a phone issue? I personally dont think so but would love to hear experiences of others.

What I havent tried is to connect to another network or wifi. IF it does connect and I can browse without any issue, that may mean that the router for some reason has compatibility issues with the phone.