Subject Can Firebird timeout / SO_KEEPALIVE options preserve connection in faulty VPN?

I have client which uses faulty VPN to connect client application (IBX, ZEOS for Interbase/Firebird) to the Firebird running on Linux. After each 7 or 10 minutes the Firebird connection gets lost. My question is - can I configure the connection to reduce lost connection?

As I understand, then Firebird sends keepalive packets every ??? seconds for the 2 hours to detect that the client connection is still active. If one of those keepalive packets can not reach client then the Firebird declare lost connection. So - maybe I can increase ??? time for technical keepalive packets? I guess that I should do this in Windows configuration and this can not be changed in Firebird.

From the other hand - the probability that keepalive packet hits existing connection is one that matters and I can not see how changing ??? time can change this probability if connection gets lost, renews and gets lost againg and so on, so on.

Actually - I have not seen such network so far, first to time to meet such network!