I think that's highly significant. Keep in mind that that's only one provider in the system. You've also got to pay the executive salaries of your hospital system, your pharmacy chain, your drug company, medical equipment company, etc.
If we figure that every company involved in your $15k/year healthcare cost is paying 0.1-0.5% of their revenue to executive compensation (Cleveland Clinic as a random example pays 0.4% of revenue to the executives, $30 million) then we are talking about a small streaming video subscription worth of cost just which is allocated not on paying a productive group of administrators to keep the lights on, but instead paying excess incentives to an extremely small group of people.
In reality, if CEO compensation was capped to something reasonable like $500,000/year or 10x the pay of the lowest paid employee, there would still be CEOs and the quality of CEOs would not decline because it would still be the highest paid job on the market. Everyone involved in our economy would be just that much richer if the wealth wasn't getting unnecessarily concentrated.
$500,000 is a lot of money, I don't want to minimize that, but it would not be the highest paid job on the market. There's a number of roles in medicine, law, finance, and nowadays software that pay more for fewer managerial duties. There really isn't much room to argue for cutting executive pay without arguing that it's unimportant to get the best people in executive roles.
And that's an argument you can certainly have, but it seems strange to make it a precondition to fixing the healthcare system, when cutting executive pay would resolve only a small fraction of the problem.