The size is dependant on how long you have had it installed and if you regularly add and remove programs. The VRDB maintains three versions to give a better means of repair after infection.
The data on my system is relatively small, nothing that isn't essential, so that could have an effect. You could try Disabling the VRDB generation and see if that helps, I doubt it, if you decide to delete the file, I would choose a different option, after disabling VRDB generation, rename avast.int to avastint.old. This would allow for changing it back if thee were any adverse reaction and/or if the file isn't created when you try the Generate Now to start rebuilding the VRDB database.
I don't know what would happen if you simply deleted on of the files (I've never tried it), avast should be able to recover from it probably by you running the Generate Now option. There is talk of some modifications to try and restrict the size of the avast.int file in a future update, when, sorry I don't know that.