Collocations for lengthy - adj.

be

extremely, fairly, very, etc.
Agreement was finally reached after very lengthy discussions.

relatively

Lengthy is used with these nouns:
absence, article, campaign, conversation, debate, delay, deliberation, description, detour, discussion, dispute, document, editorial, examination, excerpt, explanation, hold-up, illness, interrogation, interview, introduction, letter, litigation, monologue, negotiation, passage, pause, period, process, questionnaire, report, session, siege, silence, solo, spell, stay, submission, suspension, talk, tour, training, treatment, visit, wait, wrangle