The task sounds like «start the parser and wait». In practice it comes down to word choice and run mode.
How many words
At fifty channels per word, and after filtering by subscribers and closed comments, six to eight live venues per word survive. So fifteen hundred needs roughly two hundred and fifty words.
Turn combinations off
Pairing words is useful on a short list: twenty words become four hundred queries and surface things single words miss. On two hundred and fifty words it becomes tens of thousands of queries — Telegram rate-limits you within the first hundred, and the pairing degrades the topic anyway.
Split into batches
Fifty words per run. After the first batch you can see how many channels a word actually returns and adjust the rest. It also lowers the rate-limit risk: fifty consecutive queries sit far better than two hundred.
Choose words the way channels are named
Search matches names rather than post content. One or two words work — the words channels call themselves: «marketing», «crypto», «recipes». A four-word phrase returns nothing almost every time.
After collection
Run the check. Out of fifteen hundred, not all will be usable: some have comments disabled, some have a closed discussion group. Finding that out before launch is cheaper than one channel at a time in production. All of it is on the parser page.