no idea. This is why it would be useful to have the original code. I have run it using the construct that you suggest, i.e. ListPlot[Table], and it is very fast, too. If, of course, time consuming calculations are run to generate the time series, and if they are coded into ListPlot, that could give the impression, that ListPlot was slow.
Anyway, the mere plotting using ListPlot is quite fast in the Cloud.