Does the player itself fail to load? Is the player loading but failing to respond to inputs? Is the player loading and responding but it briefly tries to load the video and just gives up with an infinite spinner? Do you get error messages?
If your connection is slow or if you're dealing with large latency spikes, you can expect many parts of onramp (the interactive coding interface and the player) to be either missing or broken. You may or may not see error messages about connection problems.
If you are on a slow connection, this shouldn't be a surprise to you, as many other modern websites will be similarly unusable on such a connection. It would be up to you to determine the actual performance of your connection in order to know whether there's any point messing around with different browsers or settings.
That said, I once got an onramp video to start at ~100kbps. On the other hand, I've had trouble getting them to start in better conditions. I imagine it's just a matter of chance which particular requests time out or fail.
