SD,
Singer changed the 15 somewhere in the 50s or 60s to a more modern design. So any Japanese machine that is patterned after that is still considered a clone.
There is also clones of the 66 / 201s and the 99s.
Here is a traditional black clone:
[ATTACH=CONFIG]473854[/ATTACH]
This is my Commadore
Here is a really pretty clone:
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This is an Ambassador
Here is a different shaped clone:
[ATTACH=CONFIG]473862[/ATTACH]
This is my Coronado Princess, sold by the old Gambles Dept Store
Here is a couple non 15 clones:
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This is my SEWMOR 404. It's a clone of the Singer 66 with a bit of 201 in the mix.
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This is my SEWMOR 303. It's a Xerox clone of the 20s vintage Singer 99K-10 aluminum machine.
So, there are tons of clones out there. They are a fun way to collect different machines.
Joe