Ah, Verizon. You probably will never get any better.
They might advertise 50/50 speeds, but in the US you're highly unlikely with a starter package to ever reach the advertised 'top speed super lane' speeds as these are absolute top case scenario as if you were the only one using the internet in your neighbourhood.
Oh and the '2mbps' in steam is actually MegaBytes a second, unlike the Megabits that Speedtest uses. 2 Megabytes a second is just over 15mbps.
AC in this case would only yield better transfer speeds between devices in your local network. Your ISP is still throttling your speed wayyyy below the speed limit of Wireless AC. If you had a plan of 500/500 for example, then Wireless AC would make a huge difference over Wireless N (which is typically maxing out around 150mbps with a crowded enviroment and non ideal placement).