Tiles are imported at 1280×1280 pixels. The physical size that the tiles cover depends on the selected zoom level in PlaceMaker as well as the latitude of your model.
For Mapbox tiles, at the maximum resolution zoom level, you may need somewhere between 36 and 100 tiles to cover an areas of 1.5 square miles. However, you can dramatically reduce your usage needs by lowering the zoom level. The quality of the imagery is still very good at the ‘high’ zoom level and the number of tiles can be reduced by a factor of 4!
For example, if you need 100 tiles at the maximum zoom level to cover an area, you would only need 25 tiles if you lowered the zoom level to ‘high’. Once you click on the Imagery import button, PlaceMaker will show you (before you download) how many tiles you need to cover the selected area so that you can manage your Credits efficiently.