I would say that a 1500gp gun is a little bit too expensive for its intended use, in long lines of troops. For characters or wealthy ppl it would be a good idea. Separates the commoners from the nobles again in their quality of weapon.
I would make a gun a simple weapon. Even during the civil war people thought about training longbow units, but to be effective, they would have taken too long to train. At least as far as I heard, but the simplicity of the system compared to the training with a longbow (for use in war, like welsh longbowmen) was really one of the main factors to have gunpowder see widespread use in rifles. The hassles reloading the weapon can be learned in a few weeks.
I would make a gun a simple weapon. Even during the civil war people thought about training longbow units, but to be effective, they would have taken too long to train. At least as far as I heard, but the simplicity of the system compared to the training with a longbow (for use in war, like welsh longbowmen) was really one of the main factors to have gunpowder see widespread use in rifles. The hassles reloading the weapon can be learned in a few weeks.