You may be able to have a tailor shorten a 37 to a 33, but he will have to pull off the gauntlet placket and cut it in 4" farther up the sleeve. Some extra tapering of the sleeve may also be necessary to get it to fit into the cuff. If you find the right tailor, it shouldn't be that big a deal. If you get one who looks at you like you're crazy when you try to explain it, this is not the right one for the job. As for the collars I am not positive and I don't feel like digging out a BR shirt right now, but you may be able to get a little extra tightness by moving the collar button slightly. Many RTW shirts are built with "tie space" at the top, where the collar will not meet in a perfect V, but rather have a space in between. I have successfully moved a collar button about 1/4" up to maybe 3/8" without disturbing the lie of the front placket enough to be noticeable. If you move it too much, assuming the collar isn't already overlapping at the top, you will make the top of the placket rumple between the collar button and the second button. This might be remedied by moving the second button over a little bit, if you are still following my rambling description. So you probably won't make a 15-1/2 into a 15, but you might get it down to a 15-1/4 or so which would look considerably better. Just be sure to use a small tie knot once you have no tie space left.