11 days, no results yet. Is it possible that the Botox results will appear 'suddenly' any day now, or is it always gradual?

Typically the male "frown lines" require significantly more Botox than females since males have thicker, stronger muscles in this area. In my experience, 15 units is a very low dose for the male glabella area. You will likely need more Botox to this area. I would recommend returning to your treating physician for evaluation and hopefully a higher dose of Botox will give you a nice result. Best wishes.

I agree that in 3 to 5 days most of my pts see noticeable results. Men do require higher doses. Other possible reason are wrong injection site or antibodies if you have been treated many times previously. Best to go back to your doctor for a review.Best wishes