***Neither a teacher nor a native-speaker***
What Words Do I Capitalize in a Title?
If you check the link, you'll see what I quoted below;
These are the words that should not be capitalized;
~Articles (the, a, an), unless the article is the first or (less likely, of course) last word of the title
~Prepositions of four letters or fewer (unless the preposition is the first or last word of the title)
~Conjunctions of four letters or fewer (unless the
conjunction is the first or last word of the title)
~The particle "to" used with an infinitive (unless the "to" is the first or last word of the title)
So, it is suggested that "than" (conjunction, 4 letters) should not be capitalized.
In your sentence, the word "less" is adjective, and therefore doesn't fit the any of the conditions mentioned above(except it is of 4 leters). So, it is suggested that "less" should be capitalized.
I just intented to give you an idea about what you had asked, purely based on a link that I found on the net. So, I believe that the other members of the forums could give you much more detailed information about this matter.