i dont quite get your description... that you have 15 feet to work with ...

how about telling us the width and depth of the area ... just ballpark it..

or even better.. a pic ..

and throw in location .. just for the heck of it ...

BTW .. nothing really stops growing at some magical height .... if you can find its annual growth rate [use the latin name and add annual growth.. and you will find estimates] ... then you can guess how long it will take to get to some height.. and go right past it ... depending on how large you start with ...

also ... 15 feet high ... common ladder 8 ft .... but you dont stand on the top.. so call it 5 feet ... plus your height.. let just call you 6 foot ... but to shoulder height puts you working at 10 feet ... how will you work at 15 feet high .... so your either buying scaffolding.. or a cherry picker.. or hiring the job out.. just stuff to think about

ken

Nellie will need at least 8 to 10 feet of width...even with trimming. I've seen them easily 25 feet tall. But they can grow densely and do make a good screen.

Tell us where you live and we might be able to suggest other options.

Fosters Holly can be maintained in a smaller footprint generally, and is a bit more refined.

I think of Nellie as a very robust (wide) holly.

This is a commercial site, likely they use a manlift to shear it. It grows dense & thick because it is in full sun.

Nice picture sam_md. It's a real shame we don't have more high quality, European-looking BLE hedges like this in the Mid-Atlantic. "Landscapers" who recommend leylandiis in our climate? Not quite wanting to shoot their heads off, but close!