I'm not sure the best time to prune, now could be ok butÂ

Would you consider leaving it about the size it is, and planting some other stuff in front of it? That would be a great spot for a bed, and the holly would make a nice back drop. Doesn't seem too big in that spot.

Where I live in zone 5, I prune hollies up until the end of August. I once pruned a Meserve holly (Blue Prince) into a pyramid so you can too. Just remember that you'll get two shoots from each place you cut. Don't be afraid to prune hard; hollies love it!