When starting more concurrent jobs which are using the same slave labels the jobs are scheduled but stays in the queue for long time before new slave is provisioned.
It's described here why - https://support.cloudbees.com/hc/en-us/articles/115000060512-New-Shared-Agents-Clouds-are-not-being-provisioned-for-my-jobs-in-the-queue-when-I-have-agents-that-are-suspended

I already tried some tuning of those parameters but it still stays long in the queue.