First Sermon in Placement

I am trying to write my first sermon in my placement church that I'm going to preach on Sunday. Actually what I'm doing is unwriting my second sermon (my spell check doesn't like unwriting but I don't care). Let me explain. I am preaching at both the 8:00 am and 10:00 am services, on the same readings. At the 10:00 am service I have a 15 minute slot, at the 8:00 am service I have a 5 minute slot. Because I have prepared 15/20 minute sermons before I wrote that first, and am now attempting to work out which bits to leave out / trim / otherwise reduce, to get it to a third of the length. I suppose I could just speak three times as fast as normal, but that might defeat the object of clearly communicating something of God's word :-)

TimC