Analytics Aggregates 400 Bad Request on intervalSize

Hitting 400 when trying to pull conversation aggregates with a custom 15-minute interval. The docs say intervalSize is optional but the endpoint keeps rejecting the payload if it’s not a power of two like 1h or 30min. Here’s the snippet I’m sending to /api/v2/analytics/conversations/queries:

{
 "intervalSize": "15min",
 "groupBy": ["queueId"],
 "dateFrom": "2023-10-01T00:00:00.000Z",
 "dateTo": "2023-10-01T23:59:59.999Z"
}

The error message just says Invalid interval size. Is there a hard limit on the granularity for this endpoint or am I missing a flag to enable finer intervals?