I've sold to top retailers for 10 years and some of my sales were simple and some complex. In our experience we were selling software which allowed us some distinct value add, but in your case the buying/purchasing tracks are more well worn. Without knowing how you are currently marketing your products and how your current business development team is run I have to make a few assumptions. For example: I'm guessing you have a digital communication strategy that relays product opportunities and an ongoing fresh catalog of items for review by the stores. I'm also guessing your team carefully chooses which items to highlight to certain stores and you keep the fresh product specs and prices in your bus dev teams hands constantly. That having been said the ideal is to start to develop a pull relationship with your clients versus a push.
This includes a more careful analysis of the decision making process of each of your buyers. What is motivating them besides the coolness of the item you've got to sell? When they make buying choices some are more sensitive to categories whilst others more sensitive to customer draw. Then of course there are those that will place most anything on the shelf so long as it has big margin.
My advice is to really have your team study the drivers in the buying behavior and begin to include that in the dialogue with your customers. For example Target is seasonally motivated, but they also have a class, category and marketing mantra on a year-by-year basis or even by season. Begin to probe what Target's goal is for its customers. Move the conversation off "stuff" and into values. What you may find is that not only will that drive a deeper conversation about the buyer's awareness of his/her organization, but you'll get a sense for what types of items you may be able to present or source that you weren't currently aware of. In other words, make data about the buying process and marketing intent of your clients a critical component to your selling strategy. Then what will happen is they start to come to you to source more items and solve gaps in their offering rather than just waiting to be pitched your next items that you "think" might fit their needs.
Second, customize your digital catalogs accordingly. Allow each store or big buyer to access a catalogue that allows you to highlight the products that fit their needs the most, born from your deeper conversations with the clients.
Third, listen in on/with your sales team and understand how they are representing you. Be a second eyes and ears for a bit. Jim Collins, in 'Good to Great' often talks about being great at the basics. At $15M your temptation is to be new, innovative, and add more more more to get more sales. You may be surprised that if you become absolutely fanatical at client service you could free up an easy 5%+ growth with nothing more than an internal vision that is communicated and followed up with passion related to the client support process. (IE - understanding the buying process INTIMATELY and taking burden points off your customer is a great example of freeing up more sales too).
This combination of strategies are simply one avenue to take that could drive real growth. Customer service 5%+, Directed catalogs 5%, 180 degree change in client dialogue from push to pull 20%+. These changes could be big for you pushing you towards $20M if done excellently.
Hope this helps and please keep in mind I don't know your business, so if you are doing all these things well congrats! Let's talk about next growth items. Good luck.