Исходя из
https://trac.transmissionbt.com/wiki/EditConfigFiles - можно ограничить кол-во активных скачек\закачек:
Queuing
- download-queue-enabled: Boolean (default = true) When true, Transmission will only download download-queue-size non-stalled torrents at once.
- download-queue-size: Number (default = 5) See download-queue-enabled.
- queue-stalled-enabled: Boolean (default = true) When true, torrents that have not shared data for queue-stalled-minutes are treated as 'stalled' and are not counted against the queue-download-size and seed-queue-size limits.
- queue-stalled-minutes: Number (default = 30) See queue-stalled-enabled.
- seed-queue-enabled: Boolean (default = false) Wjem trie. Transmission will only seed seed-queue-size non-stalled torrents at once.
- seed-queue-size: Number (default = 10) See seed-queue-enabled.
Может в конкретном клиенте нет настроек для этого?