what is the advantages using lumenlab pro lens kit over lumenlab standard lens kit...isn't the pro lens kit will make the projector housing more bigger and longer because of longer focal length?

I think the main advantage is that you can use an lcd panel that is bigger than 15"

Bigger is not the point in itself. But larger lcd's have higher resolutions.

Also the long throw. Really gotta have that. The 15 inch its just too close.

I'd reccomend a pro setup if you have the money and room space.

Zoom or really adjustable throw size. As in with the fixed lens kit you have to physically move th projector to adjust the size, which is about 1:1 as in 7' wide image would probably put the proj about 7-8' away, a problem unless it's hung.

With the pro lens kit you can adjust the size so longer throws are possilble.

The pro lens is also a fixed focal length. It's just a longer focal length which allows the projector to be further back for the same screen size. The ratio of distance to screen size is still fixed, though.

The pro lens has an excellent field of focus, which results in a very clear image.

The 2 major advantages to the pro lens are that it allows use of a larger LCD panel, and it increases the throw. Both of these are bigger advantages than you might think at first glance.