Hello:

Sorry because the dalay of this answer but I need to ask also. You can look at the LaTeX Font Catalogue. If you look under the serifed fonts section, you can tell at a glance which fonts are 'tighter' than EB Garamond; not many, but what about Venturis ADF No2? Of course, it doesn't have built-in math support, but, then again, neither does EB Garamond...

In the other hand, again about typography, one of the design criteria for Times (New Roman) was to pack as much text legibly into narrow newspaper columns in small type. It's narrower than most other text typefaces, which is one of the reasons that many math publishers adopted it in the first place. So I doubt that there are many other choices that would save a lot of paper, especially if math is involved.

Perhaps the article you read was about saving ink, not paper. The statements about ink saving are dubious, but were never about saving paper, where Times indeed is designed to pack the text tightly. Take a look ath this article: thomasphinney.com/2014/03/saving-400m-font .

Finally take a look at this question: http://tex.stackexchange.com/questions/60277/average-width-of-popular-tex-fonts

I hope this can help you.

Regards