I have a few X-Wings that are more 10mm scale (Pocket scale snap together range) and also a couple of the Republic gunships from the same range, which scales a bit smaller (less than 10mm - nearer 6mm). I still intend to use them in my 15mm Sci-Fi mash up games, if only for scenery to go alongside my Captain Scarlett Angel White Falcon interceptors and UFO SHADO 1!!!
I bought them after doing a few sums in my head to work out the scale, but as they are cheap as chips I wasn't too miffed that my sums were wrong and they were out of scale...
Hope this helps:
A Corgi White Falcon with a couple of CMG 15mm Mercs
X-Wing with Merc
Gunship with Merc
Picture quality's not great as I took them on my phone and the flash was whiting out the image so had to turn it off, but I hope you get the idea.
Dave W