Did you do any preliminary root pruning this past growing season? Root ball diameter should have been established, and any roots growing outside this perimeter should have been severed by now, to force all new, feeder roots to grow inside your established perimeter. For example, a 15 ft. tree would probably have at least a 36" diameter root ball, approx. All old roots outside of the 36" diameter perimeter should have been severed with a sharp spade at the beginning of this past season. Then you'd have a root ball that will be easier to dig out when tree is moved. If I were doing this job, I'd leave the major pruning until next Spring.
In the Spring, just before you dig out the tree, and just as buds are starting to swell, but before the buds push new leaves, I'd prune away any wood that's dead, damaged, and unnecessary. I'd prune back all older, non-productive, branches to re-establish a new, basic, framework. You will probably have about half of the original wood left to move by this point. Dig out the tree, and re-plant it in a pre-dug hole, at the new location.
Without a photo of the tree, it's hard to make suggestions. I hope this may help give you some ideas. Good luck.
Frank