My answer is based on the assumption that the text is not concise and has too much information (i.e., it has something to do with the content). I am not sure if it is a matter of "space" which has more to do with reducing font size, changing fonts, reducing line spacing, etc.
It should be
Your descriptions are very clear, but it's (= the chapter/section/argument) too _________ .
Your descriptions are very clear, but they are (= the descriptions/arguments) too _________ .
One option is to use "verbose". This may require slight changes to your sentence.
Verbose (adj): using or containing more words than are necessary
- a verbose explanation/report/speech/style
If you rephrase your sentence, you can use the noun too.
verbosity (n): the quality of being verbose (= using too many words)
- Knowing they wouldn't welcome too much verbosity, he simplified his talk.
- The message is clear and concise and displays no verbosity.
You can also say "this section is too wordy" or "this section is too long".