15 Hz over 8 hours means 15 * 3600 * 8 = 432000 datapoints.
Well this is a lot. And then you are interested in every single datapoint?
How about reducing the huge number of datapoints?
Would using a single datapoint each minute be an option?
Would using the maximum / minimum within one minute be an option?
How about dividing your 8 hour one file that has all-the-hundread-thousands-of-datapoints-file into smaller but multiple files?
Do you really have to jump quickly between record-time 0:02:30,5 to 7:59:40,8 ?
I don't know a ready to use software that is better suited. One idea I have is to code your own visualisation in Delphi. There you could define a "canvas" of a size that can has a with of 432.000 pixel so each pixel will represent a single datapoint.
best regards Stefan