There can be many reasons why the text feels dense on the page, but size* is not the only factor. For one thing, you have to see it in print (if that’s the end product) to judge how the type really works because the rasterized image on a screen is influence by many factors that don’t apply in print.

I’m not familiar with Neutra Text, but a couple of things that’s worth looking at if things feel too dense is the leading (line spacing), the tracking (letter spacing) and the weight (perhaps try a light?). I advice against pushing the tracking too far, because the space inside and around letters are drawn to balance each other. If Neutra still feels too tight, perhaps you should look for another face.

*Although increasing size means increasing weight.

Sometimes increasing the distance between the words (i've forgotten the english term, see paragraph styles/justification) helps also.

In small sizes the best way to regulate color (or density as you call it) is by adjusting the letterspacing. Another thing to consider is whether you‘d use U&lc or All Caps. The latter makes for a better experience in most cases, IMO.