It's a complicated question for sure.
Let me give context I am a 6.3" (16.2cm) wrist guy on a good day.
I assume that's the 15400? Well to me it seems the watch is a little bit too big since the top lugs are hanging off your wrist. My first advice for you is to recenter the watch perfectly as a small wrist guy. It's important because we need all the real estate we can get.
You can use this video to see that the 15400 and 15500 is the same size basically. The 15500 fits wrists a little better but doesn't change lug to lug.
Second of all, watch proportion for small wrist guys is more than just wrist span. How tall are you? Do you work out? The watch may not fit your wrist but in proportion with your body it may fit overall if you are buff/thick wristed/heavy/tall.
In my opinion you should get the 15450 and 15202. They will fit you like a charm.
Here's 15202 on my wrist. It's perfect. And also the thinness of the replica makes it extremely wearable for smaller wrist guys.
HOWEVER, to deviate from your question, this is just my personal opinion, but : wear what you want. Life is too short to care. If you really like the 15500 just buy it and wear it. It's what replicas are for. Nobody outside of watch circles and watch circle jerks will point out your watch and say "it's too big for you". Wear what you like. I recently saw a thin wristed lady wear a seadweller 116600..... it was too big for her wrist for sure but if she likes it then good for her.
