This is a tradeoff I've grappled with a lot in the past 5-6 years. I was in my mid-twenties at the start of that period, and I generally have chosen money over passion. Part of my reasoning was that I could try and utilize some of that money to hire people to work on my areas of passion for me, and I could just oversee that work.
I think overall it's yielded mixed results. For me, part of choosing the money meant being committed to a full-time job, and that challenged me in ways I don't think I would have been able to simulate had I not chosen that path. The main value was the growth in a variety of soft skills -- leadership, ability to critique products and maintain high standards for quality, communication skills, overall discipline and professionalism. I think those areas of growth were a lot more valuable than the actual money.
I'm very proud of being able to financially support my family, and I probably take for granted the fact that we haven't really had to worry much about money for half a decade. So there are certainly upsides to choosing the money.
I do feel envious of my peers that have chosen their passion and been successful going down that path -- I feel like they've gotten to experience the best of both worlds and I wish I was in that group. But there are probably a lot of my peers who tried to choose their passion and failed, and I feel lucky that I'm not in that group. Ultimately, in my case, choosing the money was a bit of a hedge to ensure a middle-ground -- I didn't have to worry about failing but I eliminated my chance to get the best of both worlds.
If I could go back in time right now and do things over, I would probably try to find a way to instead choose passion, but do so with some form of strong mentorship in place to help support me from the start. Easier said than done to find the right mentorship structure, but I think that's what I'm hoping to transition toward for my next 5-6 years.
In terms of your situation, I'd encourage you to question whether the MSc is really necessary -- if your goal is to code or be an awesome SWE at a cool startup, the MSc is probably not a good use of your time.
I also want to strongly second the others in here giving the advice to not count on equity & not trust the projections they gave you. Any actual money you hope to get out of that might only be realized years away at best, and never realized at worst. You might still want to make that bet, but make sure you do so with a full understanding of how risky a bet it can be.
I actually work in technical interviewing and technical hiring so please feel free to reach out if you'd like to chat more about this topic. Email is in my profile. Best of luck with your decision!