Just a small difference in height can make a huge difference in your sewing. Here is some more information about bobbins:
The L Class and 15 Class bobbins are the ones used in home sewing machines. The embroidery machines fitted with a vertical rotary hook bobbin rely on the L Class bobbin. These machines cannot use the Class 15. A lot of the major manufacturers (like Babylock and Brother) use bobbin size Class 15.
Although L Class and Class 15 are thought to be interchangeable, they are not. A regular L Class is 5/16” high and ¾” wide. The Class 15 is also ¾” wide but 3/8” high.