As outlined in Large File Sizes in OpenBuildings Designer Projects DGN files tend to grow in size after creating drawing views.
In some circumstances BB_ACCELERATE_DYNAMICS configuration variable settings may be used to speed up the display of dynamics. Generally this is not necessary, however the following settings will change the acceleration of the file.
Unification cache is stored in drawing views and this tends to make the file size larger. You could "Compress" the file to reduce its size, but that will remove all unification cache and enhancements that are designed to speed the opening of the file. The next time the model is opened it will take a longer period of time to create the unification cache and speed enhancements again.
This is how the product was designed to work to minimize slowness in the file dynamics in the context of Dynamic views.