Fortunately it's not about being dumb, but a matter of information...

It's the capacity of the battery and that of the charger that determines how long it takes.

In theory the Pro Peak 300 should be able to fully charge a 3000mAh 7,2V pack in about an hour, depending on how efficient the charger is and if your powersupply can deliver...

A 1500Mah pack should take about half an hour, when the charger uses it's full 3000mA charging capacity.

Let me know if you have more questions, it's better to ask first instead of looking at a smoking charger....

Regards, Jan.