Photoshop. Problems saving to jpg from psb

I have encountered a problem when saving a .JPG from a .PSB. The file is saved with an excessive size and it is impossible to reduce it later. This problem has happened to me on different computers, at different times, with different files and different operating systems.
As an example, when I open the jpg saved from psb it tells me that it has a size of 25 mb but the size in the system is 172 mb and it doesn't let me send it by email.
Is it a preference?