Have your tried the built-in wifi? If so, within 10min I can almost guarantee you’ll lose a ping or more especially if your CPU is busy. Though I did find that having too many devices plugged into the usb port exacerbates the issue, especially if you use a 10′ long usb extension cable like I do. Probably a power thing, my guess is if under med-high CPU load and a few peripherals (w/o external power) are plugged in it starts shutting down power to the wifi before anything else.
I’m working on finding or acquiring a powered usb hub (which I know is kind-of the golden rule with Pi’s) to see if that helps things along.