You would likely find it useful to set the text for text boxes and labels while you're at it. As TIG says, if you find you always need to change text size to something else for new projects, you should be making a template that is appropriate for your use.
You can also sample an existing text box or other entity and apply its characteristics to new ones going forward by selecting the tool, Dimensions in your case, and hitting S. Click on the already modified dimension to sample it and go on with your dimensioning.