"E" in Kubota speak means "environmental" which is the description used for the environmentally friendly nature of the "E-TVCS" or "Environmental Three Vorteces Combustion System.
It is a precup arrangement with three zip tubes that are created by notches in the precup in the head. The fire follows the notches into the main area of the combustion chamber, as it explodes when burning.
For the unitiated, a pre cup (about the size of a golf ball) is where the fuel is first injected and a the burn begins, then it blows out into the main part of the combustion chamber. Same area where the glow plugs insert. The pre cup allows for good fuel economy and complete burn at various levels of fuel delivery and power requirements.
By the way the Japanese use the German designation for the number of cylinders as the first digit - 1 = E = ein, 2 = Z = zwei, 3 = D= drei, 4 = V= veir, 5 = F = funf and 6 = S = sechs. The 1505 indicates the nominal displacement and is not always to the exact displacement in cc but close. The suffix (B2 = SAE bellhousing) describes what accessories the engine has as a lot of Kubota engines are used in OEM applications as well as Kubota products.
Now you know