Not familiar with the model you're looking at. Is there a way to add the cruise control to the HST model? If there was, then I would recommend the HST hands down. I don't know how rough your 15 acres is, but that would give me pause without being able to put the cruise on, at least part of the time, to rest my foot/knee/leg. Some of my pasture is pretty rough, so I have to constantly vary my ground speed over that ground. The nice thing is, even though I'm changing ground speed, my pto speed is the same, and my cutters are still spinning at full speed. But when I get to the smooth patches, I can set the cruise and rest my leg, and it's pretty darn nice.
For the rest of your tasks, I think HST is far superior, even running the tiller, as you can easily change ground speed when needed on the fly, without changing tiller speed. Nothing beats HST for loader work.