Callback delay

Hello,

I have an instance of electrum deamon. Its connected to my own electrum server (48GB RAM + SSD disks). There is only one connection to it- from my client - and the electrum-server 'watch' 27 addresses from my daemon (client) wallet.

Each block is processed quite fast:

[16/11/2016-17:43:21] block 439230 (2332 18.79s) e71e055e772c096be7b4f91b7df183817156414d58a95be710e0c34d02a4e1f1 (110.03tx/s, 15.61s/block)

Load average for server is c.a 0.1-0.2.

My question is why it takes so long (25-30 seconds) to call api-callback (by electrum-server) provided by daemon after sending transaction to the network. why this notifiaction has 30 second lag when I can see that in electrum-server log information about transaction appears instantly.
I have the problem when I would like to send 2 transaction during 10-20 seconds period becasue wallet is not updated about "available inputs" and second transaction got the same input like first (mem-pool conflict appears).

How can I solve the problem to have oportunity to send transaction more frequently.

Thank You in advance for Your replies

edit: server electrum server pruning is 10000

Michael