even if it takes long time to compute it
OpenMEEG BEM computation can be long, yes.
but above all, to save in the database, I don't honestly know if it is normal
It should not take more than a few seconds to save the headmodel file in the database.
For EEG, it should not be larger than 100Mb. If it is, you should double-check which surface is selected (in green) as the default cortex surface. If it's a high-resolution surface, you may have a hard time processing sources.