I did a speed test and it said i was getting 25Mbps. I dont know about ISP throttle usage.
It should be fine with that speed and an ethernet connection. Have you unpowered AppleTV and restarted it? Sounds daft but that can sometimes correct spurious behaviour.
My internet is only 4.5 Mbps and once a feature has buffered it plays through so I don't know what could be causing your problems unless you don't get 25Mbps continuously, or perhaps contention from other users in the house/area limits internet available for AppleTV.
Some ISPs will 'throttle back' their speed after a data quota has been reached or at busy times - the terms of your internet contract would detail anything like that but I suspect this is not the issue.