a) The web standard is one blank line after a paragraph. So you cannot add extra space by hitting return again like you could do in a word processor: you need coding in the so-called Text editor.
b) The exact amount of space below a paragraph (as well as between the lines of a paragraph) is part of the default styling of the theme, and it varies from theme to theme. So you may get different results if you switch to a different theme, and you can change the default styling once for all if you have the Custom Design upgrade. But if you want to change the styling here and there, upgrade or no upgrade you need coding again.
At first I misunderstood your question, because I saw you mention "what Word would call 1.5", which refers to line spacing. Now that what you meant is clear to me, the link you needed isn't the one I originally gave, it's this post of mine:
To tailor things to the theme you're using, when you want extra space below a paragraph you need to code it this way:
The default in the theme you're using is 0.7em below as well as above a paragraph, so 1.4em will give you 3/2 of the original space between paragraphs. Obviously you can change the number to adjust the space.