same cube different distinct columns size

I have a cube A which generate 828kb in the step 4 (extract fact table distinct columns) another cube B is the cube cloned by cube A,however ,this cube generate 2.6G in the step 4.Both of them are same strure and have same previous step (step1,2,3)

How solve many cube use same UHC dimension?

I have mutiple cubes which contains some same dimension such as date dimension and user dimension , user dimension is very large dimension which contains 1600 records.When I build cube ,this step( Build Dimension Dictionary ) would cost a very long time . could it be possible to build one