Internet speed sporadically drops for a few minutes

Over the past 2 weeks I've been encountering, at inconsistent times, periods (a couple minutes long) where my internet speed (tested through speedtest) will drop from the normal ~15 mbps to under 2-3 mbps and completely halt any task my wife or I were working on. A reboot of our Netgear AC1900 C7000 hasn't yielded any changes. While this is a livable annoyance, I'd still like to get it resolved, as it results in my personal game server booting people unexpectedly and sometimes repeatedly.

Any help would be appreciated since chatting with an agent is currently unavailable.