I think it constitutes lots of things so hard to pin down. Mine doesn't run quite as high as yours but its typically either the top or second top user on battery stats on my phone. Its been like this for me ever since Jelly Bean and I can't figure out how to reduce it despite trying pretty much everything I can think of, including factory reset and resetting up from scratch on several occasions to no joy.
What device, country, carrier, software version are you on? I'm on 4.1.2 on Three UK. If you are are also then perhaps its something in the Three software as I don't see many complaints about Android System around yet it seems unfixable to me!
