1. Start by opening the Measure Tool and measuring the object.
2. Next, go to your commenting tools and make a new text comment. You can use either there regular Add Text Comment tool, or the text box tool. Basically, we're just need to use one of the tools that gives us access to the text properties editing. Then using the Text Properties tool, type in the distance that Acrobat generated above when you measured your object. In this case, it is 1.5 in. Then change the font size to whatever you prefer. You can change the color as well if you like.
3. Next, select the text n the text comment you just made. Copy it.
4. Open the Comments pane. Select the distance measurement in the "Line" comment.
5. Paste in the text that you copied from the text box tool. Violá! Larger type!
Now, I wish there was a way to make this the default, but since Acrobat doesn't have text size as one of the editable properties of the measure tool, the size of the type isn't taken into consideration when you choose "Make Properties Default."
However, you can have access to edit a number of other properties of the Dimension Line, just not type size. If you need to have larger type Dimension Line type on a regular basis, I would imagine that an Acrobat scripter could easily write a script to do just that.