Started my first barleywine last month. Not going to even think about moving it to serving keg for at least a year (it's going to move to an aging vessel once the yeast is done with it, which it's not yet). It's going slow due to the lower temperatures I'm fermenting it at. I emailed White Labs about the temperatures it is at to find out what to expect. With WLP099 at lower temperatures, other than a longer ferment time, I should get a much better flavor profile. Especially compared with what others have posted about it. I'm on target for just over 15% too.
Will be interesting to see how it is once it's moved to serving kegs. Planning on using small kegs for this. Most likely my two 2.5 gallon and one of my 1 gallon kegs. No carbonation worries there.