If you're not getting what you should then most likely you have congestion in your area - maybe a load of people torrenting - or some issue otherwise on your line. You should call if you not getting what you should and speak with Tech Support and not just the customer service people. Get a ticket number for your issue and press it. If you not getting your speeds you should also get a rebate after the issue is resolved.
Supposed to be a 20Mb connection so 15+ not bad - and it's shared with my phones and mine and my wife machine and laptops.
Knowing the solution doesn't mean knowing the method. Yet answering correctly and regurgitation are considered "learning" and "knowledge".