The 15K were made later into the 50's-60's than the US machines, I suspect yours is one of the later ones as it has the updated logo Plate, and also the gold highlights around the stitch length circle. My later made 15K-75 has the gold highlights there - but it's the "next generation" from yours.
I've seen way more variations in UK made machines, and more that came with a spoked wheel as hand cranks/treadles stayed popular over there way longer than they did in the US.