I think an iPhone 6 is causing connection issues with other devices connected to my router (with Ethernet), how can I avoid it? I have a MacBoook Pro with OS X 10.9.5 connected to my router with a Power Line Connection and Ethernet, which I did because I use the laptop to play an real time online game which needs mostly a stable ping and no ping spikes, and using WiFi at a distance was deteriorating the gaming experience.

The problem is, someone in my house has bought an iPhone 6 (after I installed the PLC, so I'm not quite sure if the problem arises all the same if the MacBook is connected by wifi), and by trial and error I highly suspect that it interacts with the internet connection to other devices. Whenever the phone came home, if I was playing, the connection went nuts. Not that ping went high, but overboard. To the point of not being able to navigate normally either: websites, youtube videos, etc. I mean, charging any light website shouldn't need that much speed, and still it doesn't work.

I would think that it's not possible that an iPhone 6 with a few apps, which sometimes isn't even transmitting any significant data, could take up that much bandwidth (the local connection is supposed to be around 10Mb/s, and I've been able to enjoy 1,5Mb/s download speeds with torrent). 

So I don't really know what the cause is, or how to solve it. Is it truly a bandwidth problem? How does the router determine how much bandwidth is allotted to each device/output (wifi/ethernet)? Could I change the router settings (it's a normal low-end router given by my internet provider) to make the computer a priority, so that the iphone only takes reasonable/excess bandwidth?
Troubleshooting is basically a process of elimination, but this one may be a little hard to do through the comments, so here we go.

TEST 1

Let's start by doing this test:


Switch Wi-Fi off in your iPhone settings (not just disconnect). 
Totally shut down the iPhone. 
Use your Wi-Fi as usual to play your real-time game for about a half hour and make a note of the results.
Switch the iPhone back on but do not switch Wi-Fi back on.
Use your Wi-Fi as usual to play your real-time game for about a half hour and make a note of the results.
Switch Wi-Fi back on in the iPhone and connect it to your Wi-Fi.
Use your Wi-Fi as usual to play your real-time game for about a half hour and make a note of the results.


After following the steps of test 1 you should have three sets of results to share back. This will greatly help you and the community to narrow down your problem, one way or other.

TEST 2

Okay, Power Line adapters are notoriously 'fussy' and it doesn't take much for something to interfere with the quality of their connection. Let's do this test:


Disconnect both ends of the Power Line connection, totally removing them from power etc.
Connect your MacBook Pro directly to the router via ethernet.
Ensure the iPhone is not connected to your Wi-Fi and play your real-time game for about a half hour and make a note of the results.
Now make sure the iPhone is connected to your Wi-Fi network and play your real-time game for about a half hour and make a note of the results.


Let us know the results.