You can cut it back to a few feet now, and then hard down to a foot in March. It will then probably grow to 8 ft again next summer, and flower in August.
If thats too big, take it out and plant either a buddleja Buzz, which is dwarf, or something else altogether.
I chop them right down to knee height every spring.
I'd wait until Spring to chop it.
I usually cut them back roughly in November, to avoid wind-rock loosening the roots in the winter, then cut them right back as I said, to knee height in the spring - pruning to an outward facing bud and taking out very thin or crossing branches right out.
I prune mine hard in March
The groundsmen at work can - but they're the exception that proves every rule
I have a tree and two shrubs both 15ft. All three fifteen feet. Can I prune the - live in the N E of Scotland?
I have just pruned mine today,I prune quite hard ,some people leave it later but I do it now so the seeds dont seed everywhere too much.