there are three things that govern planting distance on apples.
First is the rootstock the trees are on and the soil their going into.
Second is the shape you want the tree to be.
Third is the height you want your tree to finish at.
Luckily you've chosen the best distance that will accommodate all these requirements.
If your rootstocks are dwarfing or semi dwarfing...then you can let them grow as strongly as they can..filling the space as best they can. Though stocks of 9 or 27 may struggle.
At that distance you can have centre leader or open bowl trees
All our old plantings of the 50's and 60's were at fifteen feet square and these were large open centre trees that were on the old type 2 stocks which are fairly vigorous compared to modern ones. However if you are using the more vigorous ones you will have to be prepared to keep the pruning tight once they are full grown.
I would add here that the varieties chosen can have some bearing too.
Most triploids are more vigorous than normal vars and will need more careful pruning. So Jonagold, Crispin, Bramley etc. would need more attention.