ok now that I am awake . First let me say I am not bashing I am trying to help. You have 15 feet. you need to come in from the side a min. of 3 feet. You have 3 main plants that dont work in the small spot. the Juniper I am guessing it will be a spartan. will grow a Min. of 6" a year. they tend to grow fast when they are in a topiary to fill in its normal shape. I trim Topiary shrubs two times a year here where I live and you can get close to 12 " of new growth a year. second nandia is a moderat growing plant. the growth stamp will say 4 to 5'. that on is from the center of the plant. I have some I planted and its from the center. so thats a 10' plant. the loropetalum, well you can get a cutting or a seed or a root growth plant. only one will be a true dwarf. and you will not know until it starts to take off. some times they just revert to a normal one. So instead of me finishing my little golden book. let me simply say. you dont have the room. no mater how good it will look fresh, in time it will need pulled. and I guess that would be in 5 years if that. some day when you fine a place for this design it will work. Just out of curiosity do you have a horticulture degree or a landscape design degree?
so i have , 6' sides , 10' lor, 10' nan and a trimmed 5' wide juniper =31' with trimming you hurt the look you want with a topiary next to the other plants. and if its shady it will look that much more open. the look you want next to topiary should be a full formal shape. there is now zin here. smiles.
remember not bashing trying to help. you asked.