Hi Sal,
Thank you for the interest. Unfortunately codecanyon (or seller platform) does not allow promo/individual discounts nor promo codes, only global discounts for everyone.
Our next discount period (20% or 30%) is scheduled for the summer, sometime either july or august. A more significant discount is at the cyber week (usually 50% or 60%), that is at the end of november each year.
Unfortunately we are planning to increase the plugin price very soon (around mid march), similarly to almost everyone on the market due to the current global financial situation. It happens very rarely, last time was about 4 years ago, so we are trying to keep the price as long as possible, but it looks inevitable at this point. It should not be a big increase, around $3-6 per license, but I thought I let you know, as it can be a significant cost for 15 licenses.