Keep in mind that the chargers that come with any particular model are intended to be used only with that model. Given that you can use a higher wattage charger with a computer that comes with a lower wattage charger, but not the other way around.
So the 85 watt charger for 15" MacBook Pros could be used to charge a 13" MacBook Pro or MacBook or MacBook Air provided they all used the same MagSafe connector. But the 45, 60, or 65 watt charges should not be used with a 15" MacBook Pro. These chargers cannot provide sufficient wattage. Although they can charge the battery they will take considerably more time to do so. Furthermore, if the computer undertakes tasks that run the CPU and GPU near their maximum levels, there will be problems because the battery acts as a supplemental power source when the computer is connected to AC because the chargers cannot supply sufficient power on their own.