Well, to begin with, you'd need to tell us what size battery you used, what voltage you would combine them into, and what the amps of the controller is. I have a controller on one bike that has a pretty 1500w label on it. But it's pulling 3000w routinely.
Assuming 24s, 3 5ah packs would give you about 100v 5 ah. Ride time would be less than 15 min if you ride full out. Youd get about 30 min from 24s 10ah. And if you used 15 ah, you'd get about 35 min, because you'd melt the motor before you discharged all 15 ah.
But I'm making an assumtion here. I'm assuming you'd be using a typical 100v 40 amps controller, which is about 4000 w potentially.
But if you are talking about 15 ah of 6s 24v, then things would be quite different using just 1500w.
Things would also vary depending on how much you rode up and down hills, headwinds, and what top speed you cruised at. The same presumably 300wh could last 3 hrs at 100w, or one hour at 300w, or 20 min at 900w.
FWIW, 400 w will get you cruising at about 20 mph, but 30 mph tends to take at least 900w.
