The videos in your Media folder I can stream/play without needing to buffer here (Using 2.8MB/s of download). The video on your homepage in order to cut down on the file size, you could recompress it down to a lower resolution but maintaining a bitrate that keeps the clarity of the video, thus improving streaming "speed" on slower connections. Other than that, you're basically up to whatever the server is able to kick out at the time, and Internet connectivity between your PC and the server.
Looking at your video on the home page, it's 720p30 at an 8Mbps Bitrate, total file size for a video length of 28 seconds is ~27MB. Cutting down the resolution to the video player size of 399x224 pixels and reducing bitrate should help a bit.