Answer: Trimming it will only delay the inevitable. A plant that wants to be larger than its alloted space is a constant maintenance problem. You would do well to consider putting another plant in that location - one that will not grow to hide the windows.
If you choose to trim it, do that now (at the end of winter). Cut it about a foot shorter than the height you want it to be kept at. Then when regrowth takes off in spring and summer, trim it back every few weeks to 6-8 inches above the original cuts. This will likely create a very different look to the plant. Not to mentions a quickly impatient gardener!
Thanks for the question!
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