Do you always disconnect after 15 minutes no matter what you're doing online or does it just happen with Aces High?
That's a good question. If the answer is yes, then it might be a lease time issue.
If the answer is no, here's some other questions and probable answers:
Does this only happen while playing AH? If yes, then might be related to the ports or something else related to the game.
Does this happen while passively using the Internet, like watching a Youtube video longer than 15 minutes, or reading a long single site for more than 15 minutes? If yes, check the power saving settings of your network card(s) in Device Manager. Also check other instances of Power management in the Control Panel. Uncheck "Allow the computer to turn off this device to save power”. Choose the "Maximum performance" power scheme. Disable hibernation and maybe sleep mode, too. Make sure every network related option in the Advanced Options is set to be always on.