Spier and Mackay Shirt Sizing

Hello, about to buy a few shirts and am a bit concerned after reading that Spier & Mackay tends to be smaller than people expected. I measured myself at 37" chest, 34" sleeve. 5' 9" 155 for reference. I also have a dress shirt from Calvin Klein which is a 15 slim which I think fits well.

I'm planning on ordering 15 contemporary, can I get a sanity check on that? Would 15 slim be too small? Here is their fit guide https://www.spierandmackay.com/fit-guide/size-chart-sportshirts
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