Getting uncomfortable after remaining stationary for 15 minutes is normal. Your body is telling you something - being stationary is the enemy. I think trying to optimize your chair is the wrong solution. Instead the answer is a diverse work environment you can move around in and continually adopt different postures! My favorite work environment is a carpeted floor which I can lie down on, crouch, sit up, work at a coffee table, or even pace around. Any one of those postures would probably get uncomfortable after a while, but I cycle through them too quickly. Admittedly this probably wouldn't work well for work involving huge amounts of typing, such as long form writing - but for the kind of programming and data exploration I do it's great! I've always been a fidget, and being able to fidget with my entire body feels like I'm finally embracing something I was always meant to be doing.
This working style has only become practical in the last decade or so, with the advent of very light computers with excellent battery life, and I don't think we've culturally caught up.