Too long commentary to Eduardo França. In Brazilian Portuguese, "Preguiça" is usually something in the person (in this case the reader) that may prevent doing something; the "tl;dr" expression makes assumptions referring to something in the environment (as far as I know, in the writer); text was too long, so it is not related to the reader willingness. Of course, when no explicit criteria is used, and depending on the circumstances, someone claiming a "text was too long" might be revealing lack of will or laziness when the text in fact was good and justifiably long.
Considering this previous observation, I would say yes, "preguiça" could be used to tag the behaviour of people claiming, unjustifiably, that a text was tl;dr. However, I would say no, "preguiça" is not the expression the OP is looking; as a correlate of tl;dr.
Now, answering the question, as long as a similar expression in Brazilian Portuguese can't be found, I would translate tl;dr as follows:
- [por ser] muito longo, [por isso o texto] não [foi] lido.
- [o texto era] demasiadamente longo para ser lido.
- [o texto era] injustificadamente longo para ser lido.
Those translations emphasizes the length of the text and not the felling of the reader. On the contrary, the following emphasizes the reader, the person:
- Muito longo, mas eu simplesmente não quis ler o texto.
- Muito longo, mas não li o texto por pura preguiça, [embora o texto fosse interessante e bom].