What a waste of bandwidth. If you've got users with limited and/or slow connections, I'm sure they'd be thrilled that you're trying to perform miniature stress tests on their connection. Why not save that bandwidth and waiting time for actually loading content they want? Just lazy load the images. Problem solved.
Edit
Not to mention as someone else has said, the results you'd get wouldn't be realistic at all; intermittent connections, going under a bridge, network lags, etc. I dare say devices are also smart enough to realise when something is trying to hammer the connection, and so will throttle it.