With 15y exp, surely you shouldve absorbed significant higher level knowledge long time ago. Why didnt u use that knowledge to do more complex stuff and prove that u can work at an advanced professional level?

I have seen some assistants become Chief of Staff / Project Mgr solely due to the amt of business knowledge they absorb from their bosses. And not due to nepotism as well. When working with them, they are genuinely sharp thinkers.