Pilgram, is the tension assembly on the face plate of the machine? If the tension assembly is on the face plate, you have a model 15. There are a few errors in Singer's serial number data base - it does happen, but very rarely do we see an error.
If the tension assembly is not on the face plate, but instead on the head where you 'commonly' see the tension assembly then go to this site to figure out what machine you have.
http://stores.ebay.com/Sandman-Colle...-Template.html
What decal does the machine have? Is it a redeye, or lotus? Those were only used on the 66. Can you post a photo?
Nancy