BKR15E is a much colder plug. With NGK, the higher the #, the colder the plug and vice versa, but for most other mfgs, the higher the #, the hotter the plug. If you get fouling come winter or notice alot of carbon building up, go to a hotter (lower # BKR#E) plug. The rest of the letters should be the same as they describe the length, thread size, and electrode specs.