I have about 3.5 acres and only a couple of ponies that aren't allowed grass in spring, summer or early autumn, and I'm down to 2 ewes (old, one is on its way out, in fact) so can relate to your problem.
However. 1.5 acres is so little. I wouldn't buy any kind of machinery for it. I'd do one of two things. Either, I'd rotate it all a bit quicker (or not at all...older ewes are less likely to need as much worming and you can do fecal counts on them anyway) or I'd use an Austrian scythe on the paddocks I wanted topping.
I mow all my weeds with a hand-held scythe rather than bother getting out the petrol-powered, noisy horrible trimmer. Here is what I did in less than an hour. Where it is shady is where there used to be weeds up to my head. Where it is sunny is what I did after I took the photo.
My scythe cost me just over £100. I love it. I use it all the time:
http://www.austrianscythes.co.ukHaving said that, topping was necessary in my field this year and last due to the lack of sheep. It's okay, but if you don't do something about the rows of mown grass on the remaining grass, it kills it. I wouldn't want to mow 3.5 acres with a scythe but I'd do a fair amount of it before I'd shell out money on machinery that then needs as much upping as the darn grass!
Tell your sheep they need to eat more, LOL!