Imac getting slow when connect to the internet/wi-fi

My imac getting slow when connect to the internet if I'm using wi-fi. It's not happen when I used mobile hotspot to connect the internet, everything went normally, but if using wi-fi the problem appear again, I already tried to change the DNS, but it's getting normal only on couple days, after that the imac get slow again, especially in opening adobe software and google chrome.

Anyone have same problem or know how to fix it? Please help. Thank you.