Nothing else in the dev kit has lagged me until I tried to use this tool. It has a huge delay until it completes smoothing but it’ll smooth horribly. I know I don’t have the most perfect computer for running this dev kit (pretty much a toaster) but is there a setting I can change to perhaps eliminate the lag? 
Making it smaller is probably the only thing that will reduce lag. It’s a pretty CPU intensive tool so you’d have to live with the lag if you computer can’t handle it. That said, I never noticed any lag at all on either my very old i7 930 or my new i7 4930K so that might give you an idea if it’s because of your computer or something else.
Probaly not relevent now, but if anyone else wants to know, I had the same problem and the solution was to turn down the Filter Kernel Scale to 0 in the tool settings.
you think smoothing is bad, wait until your trying to paint your island with trees and bushes and grass lol. I am to the point wher ei get about 15 seconds delay in every click to add 5 trees.
64GB ECC RAM … 8 core/8 virtual (16 core CPU) … my computer laughs at ADK … until i have about 10GB RAM spent on the map alone … haha. Give it time, you add enough stuff, your computer will stop loading your map (since you have issues smoothing already)