I also started with 15# (a pretty red "GoFit" KB: Target and Dick's Sporting Goods carry them).
I think it was a good place to start (recommended starting weight is usually 18# for most women, 25-26# for strong women, but that's just because that's the size standard kettlebells come in--a bit under 18# and a bit under 26# because they are weighed in kilos).
More recent recommendations I've seen recommend anywhere between 15# and 26# to start, for women.
No matter what you start with, there will be some moves where the bell feels too heavy (like Turkish Get-Ups, which you might start with NO weight, then with a light dumbell, increasing weight until you reach your KB weight), while it will soon feel light for others (like swings, which I find are easy to increase weight on...if you don't want to increase weight, increase number of reps and/or speed--up to a certain point for the latter).
I now have bells in 15#, 20#, 25#, 35# and 45#. With Lauren Brooks workout, I've been using all but the 45# for different moves (though the second time I did the workout, I didn't use the 15#, but used 20# as my lightest).