Impossible to tell if you could shoot a shorter LOP well, or better, without seeing you mount the gun and shoot some ........ or at least knowing your sleeve length and the LOP on the gun as is, and how thick the spacer is (looks to be nearly an inch). Your friend either has much more knowledge of your physique and shooting style than we do, or he is being a bit presumptuous, IMO. I am 6' 2" and shoot guns with 15" LOP quite well. I was fitted with a try gun many years ago and the resulting dimensions were almost exactly what I had already determined through trial and error were right for me. My sporting clays gun, which I shoot premounted, is 15 1/2". Most people have shot off the shelf guns for so long that when they mount a gun that is actually the right LOP for them they think it is too long. In the newest issue of one of the clays magazines there is an article that is entitled something like "What are the Pro's Shooting?". Though that may not be the name of the article, the gist of it is that they interviewed ten of the top sporting clays shooters in the USA. I scanned over it quickly, and can't find it at the moment, but the thing I remember was that they asked all of them what the LOP is on their sporting clays and FITASC guns. I don't think there was a single man that shot less than 15", several going up to 15 1/2". Before anyone cries "Foul! they all shoot premounted", I say "Not in FITASC!". And I have met several of these guys and they aren't all over 6 feet tall, either. Some are considerably less than 6 feet.
The gun looks well used, by the looks of the checkering. If it were mine I would shoot it as is, if I were convinced I shot it well and it doesn't hang up on your vest or coat who mounting. If you want to make that extension invisible contact Mark Larson at marklarsongunart.com. He can put you on an extension and blend the grain with paints to the point that it is impossible to detect.
Good shooting, SRH
