The more trees and obstacles that you have, the more time you will save with lawn tractor vs CUT. I have 2 tractors and 2 bushhogs and I find that I can mow my place (11.2 acres with about 5 that I mow) faster with the 55" zero turn mower or the JD 54" lawn tractor than with either tractor 6' or 7' bush hog. I have a lot of trees and mowing around them with the tractor is mostly turning and crisscrossing already cut sections just to get a small patch and then end up using the lawnmower anyway to get around the trees some of which are so close together that the tractor wont go between them. Of couse I dont have all the weeds that you have, but after one cut, that should no longer be a problem. My take is to try it with the lawnmower but eventually get a tractor and bush hog or other type of mower as the homeowner class of lawnmowers are not designed to stand up to cutting 15 acres and unless you get a $15-20K commercial mower they will be toast in a short while. For that price or much less, you can have a nice CUT with FEL and a few other attachments