You should be able to find folding step ladders up to 16' tall. They won't be cheap though, and they are fairly heavy to move around.
Try this: go to
www.sherrillinc.com, and search for "articulating stilts".
I used drywallers stilts when we hung Christmas decorations last year, and they saved a bunch of time over a ladder... The ones at Sherrills can be adjusted a little higher than the drywallers stilts...