My opinion is don't worry about the percentage you put away. Figure out what you want to retire on, what you will receive from that (always back them off a little to be safe) and then figure out how much you need to put away. Maybe you need 40% put away to get there, maybe 10% does. Don't say 15% is the magic number, because you could end up with 30k/year or 300k/year when you retire. Get the number you want to retire on and work from there.
And probably don't underestimate how long you might live unless you have a family history that clearly indicates a likely shorter life expectancy or if you have really bad habits.