The quality of the land will affect its popularity as smallholdings. If it's suitable I would have thought the 15 acres would have been snapped up as is, if the price is fair.
Is the ground sloping too much for machinery?
Is it acid or wet, good soil or poor?
Is it miles from human habitation?
Is it pasture or arable land, well maintained or derelict?
Is it infested with noxious weeds such as thistle and ragwort?
Is there any chance of the buyer ever being able to get a house built on it?
Planning permission might be needed for change of use, and even for shipping containers.
I really don't see that dividing the ground up into smaller paddocks or holdings is going to make it more sellable, unless the answers to the points above are all positive. It does sound as if he may be over pricing the place for what it is. If not then it would have been bought quickly to add to someone's existing farm, a neighbour perhaps.
I don't think you can (or should) give him business advice unless you are familiar with the field and all the circumstances.