[Koha] Saving MARC records very slow

I'd like to ask one question. When I am saving MARC records in Staff Client, after clicking the butto "Save", normally it takes 10-30 seconds in which the web browser is frozen and seems tdoing nothing. Afterwards it saves the record. When I do the same operation directly on the server, it is much faster - it takes only 3-4 seconds. But I can't let cataloguers work on server. Would anybody know what could be the cause and how could I fasten it? Thank you Ondrej Mlecka