The cabinet is 46" long (when extended and machine is up) x 29" tall (not including the machine height) x 16" deep. The manual with the machine says it is for 15-88 and 15-89. I believe the cabinet is made of walnut. I do not see any major defects or blemishes that I need to disclose. The cabinet has five drawers: The four on the sides of the cabinet and one long separated drawer below the machine well. 

Singer Serial Number Database ISMAC

Singer Treadle   linking to another good blogspot

LETTER:                                            AF   

Register Number:                              91806 - 126805

MACHINE CLASS  MODEL #       15

DATE ALLOTTED                          November 21, 1938

The Singer Model 15-88 was the last machine they designed specifically for treadle use. It was supplied in a somewhat modern looking treadle with steel or occasionally wood sides, a bit smaller than the older ornate treadles. It was equipped with built in lever stitch length regulation and reverse, plus lowering feed dogs. The Class 15 action is a good strong one. This machine uses standard needles and standard low shank feet, and will accept all of the modern piecing , even feed and darning feet. If you can find one, you have virtually the best of all possible worlds from a treadle user's standpoint.
So, what are the disadvantages of a 15-88… basically only aesthetic… they are the typical plain black Singer, and the treadle is quite simple in appearance. They were marketed from the early 1930's into the 1950's.

The Model 15 was made as a hand crank, treadle and an electric machine. An industrial version - the Model 16 was also made.

Model 15, introduced in the 1880's and continuing into production today. The Model 15 series features a removable round bobbin in a bobbin case mounted under the needle vertically… quite different from the shuttle bobbin machines. The oldest version commonly found is the 15-30. It has a lever stitch length control, but no reverse. This is a somewhat better built machine than the shuttle bobbin models… it was more expensive in it's day  (Dick Wightman)