Didn´t wanna wait anymore so I just did it.
Here´s jdm1 slimmed down from 230kb to 6kb:
http://filebin.ca/benqxp/jdm1_fix.map
What´s changed:
1. Removed all embedded graphics and referred the layers to their external counterparts. This is the main thing.
2. While I was at it I erased tiles on layers behind other layers that won´t be visible anyway. I imagine that makes the map easier for the computer to draw, though probably not by much. Can´t hurt, in any case.
3. Removed the extra background layer of shadows and added those shadows to the foreground shadow layer. There is no need for two shadow layers, you can have it as foreground while still being behind the main tiles simply by ordering the layers right nowadays.
4. Changed so the brown backround tiles get invisible with high details off. Didn´t seem like essential graphics to me.
5. Also removed the nametag. Sorry about that, but otherways the file would have been on 23kb or something . Plus it wasn´t visible in the original anyway (it was placed behind the main tiles).