Why Do My Download Run Slow When I Download Stuff From The Internet On Sm-j327p ?

Why do my download run slow when I download stuff from the internet on SM-J327P ?

 

It depends on what internet connection you are using - a WiFi connection or a Mobile (Cell phone) Data connection, and whether the Cell Phone Data connection on your phone supports is 3G or 4G and the coverage available in the area when using. The WiFi connection speed will also depend on what that WiFi connection supports - whether it is a home residential internet connection or a public WiFi spot.
Read here on how to test your smart Cell phone speeds:
https://www.howtogeek.com/215488/how-to-test-your-internet-connection-speed-or-cellular-data-speed/