Leave cushy job for startup? I will not promote

I am a lead engineer / manager for a medium-sized company. I have been with the company for four years. Compensation and benefits are very good for relatively easy work. Vacation is five weeks with an additional week of sick leave. It is a relatively stress-free work environment and the work / life balance is a dream. My friend formed a startup and is closing on a $1.5m funding round. He offered me a position with 5% equity. The caveat is the salary and total comp is half of what I currently earn. One positive is his former startup had a successful exit. IMO the idea is pretty solid and the new company has a lot of potential. I am torn on what to do. I am very comfortable in my current role, but I am bored. This is an opportunity for me to build something new and exciting, but I will be making significantly less money in the short-term. There is the potential for the 5% to be worth millions in the future, but the odds of it being worth nothing is greater given that most startups fail. Is 5% even enough equity to take such a significant pay-cut? I will not promote