Scala Stream Collector: bump to 0.15.0 (closes #3983)
Scala Stream Collector: bump to 0.15.0 (closes #3983)

liveintent-berlin/snowplow,liveintent-berlin/snowplow,RetentionGrid/snowplow,liveintent-berlin/snowplow,snowplow/snowplow,RetentionGrid/snowplow,RetentionGrid/snowplow,liveintent-berlin/snowplow,RetentionGrid/snowplow,snowplow/snowplow,liveintent-berlin/snowplow,snowplow/snowplow,RetentionGrid/snowplow,snowplow/snowplow,liveintent-berlin/snowplow