Hmm... I verified in the connector it's parsing that 20150528.163102 to create a timestamp (it reformats it to 2015-05-28 16:31:02), so it's weird that somehow it's being timezone adjusted. Usually that'll happen if the LEM appliance is in a different timezone, but then I'm not sure why InsertionTime in general is correct.
Are you receiving other data via syslog on the LEM appliance? Timezone/timestamps are correct on those?