'Micro' or 'Mini' pigs or exactly that when compared to fully grown farm pigs.
In the UK, many pigs are slaughtered for meat at just 15-16 weeks of age when they have reached a weight of 55-62 kg.
Source: RSPCA - The welfare of pigs information sheet
With this fact in mind, it's worth looking at the difference in size of a micro or mini pig compared to farm pigs of the same age.
Below is a micro pig at Petpiggies pictured at just 3 days old and and again at 15 1/2 weeks of age
Below we can see the difference in size and weight of a micro pig at 15 1/2 week compared to a farm pig of the same age
Here are some more pictures of a micro pig at 15 1/2 weeks of age.