Having painted a few 15 mm figures (thousands), I use this method for my North American original peoples: a pinkish skin tone followed by a thinned wash of red brown, vary the red brown if you like since there is variety. Then I paint the rest of the figure. I follow the slop it on method better known as layer painting, from skin outwards. First steps are not neat but each progressive step gets neater and neater. This is not the way to win contests but is the way to paint lots of figures quickly.
Oh, and I don't generally use the obscenely expensive "Hobby Paints." I use plain old craft paints, thinned when needed - only sometimes, which cost about 1/20th as much by volume as those other paints. My most frequent exception is I do buy metallic Hobby Paints, but craft ones also.
I have many hundreds of 15 mm Plains warriors to paint my self but not just yet.