This is a very natural, very common, place to end up in your role. And it's not uncommon for CEOs (and especially those without a hands-on tech role) to view product development purely as a cost center and to build out sales and marketing disproportionately (not least from the point of view of the engineering team).
15% with 4 year vesting sounds ok, if not great, for the situation you've described.
I agree with one of the earlier posters: you should produce a roadmap of what you believe needs to (not should, not could) be done and document the level of effort required to achieve that, in combination with the misc IT and operational work. Include in that roadmap the time required for recruiting and training the people you believe are required, both initially, and considering ongoing turnover.
Share that with your fellow co-founders / management team, and strive to get buy-in to the necessity of achieving the goals you outline. Depending on the context of the organisation, it might work to present this as a natural part of the growing maturity of the company? Sort of a "While it's been fine to two people in a corner thus far, we're reaching a point where that's holding us back, and here's a plan to take us to the next level".
In my experience, the sales team will be very supportive of anything that gets them more to sell: every extra feature, every refinement, etc, gives them another opportunity to grow the addressable market, or to satisfy another potential customer, etc. If you're able to get them involved and bought-in by getting some pre-presentation feedback on the roadmap, it might be worthwhile? You don't have to just sell this to the CEO: you need to have the rest of the organisation selling it to the CEO as well.
If your proposal is accepted, all is good, and in 12 months you can use that as negotiating leverage to get more equity :-)
If your proposal is not accepted, even in some inevitably cut-down form, what is then entirely implicit, with no threats or rashness or backing people into corners, is that it's kinda obvious that your personal point of view and the general company's point of view have diverged. And that's the time to start looking for a new opportunity.
Getting a new job in your situation is a whole other post, but if college is an option for you, now might be a good time? Otherwise, carry on in your current role but pay much more attention to networking: go to meetups, contribute to some open source, start blogging, build relationships with customers of the business, etc. It'll likely take 3 to 6 months to find a good new role, so set your expectations accordingly, and work every week towards that as a personal goal. You'll have to take time away from your current over-worked situation for this: but you need to prioritise yourself over the company, and this is the perfect way to start.
Best of luck!