Hi Nick,
Thanks for your response and sorry for my English 
With latency I mean delay between sending command from smartphone to writing HIGH/LOW to digital pin on Arduino. I don't need to transfer big data all I want is to have the lowest possible delay between these two actions.
To sending data from smartphone I use some of bluetooth terminal apps like this: https://play.google.com/store/apps/details?id=project.bluetoothterminal
About 115200 baudrate, I also try to change it to 4800, 9600 and 38400, but I didn't notice any change.
As well there wasn't any progress after changing SoftwareSerial(53,52) to Serial1 on pins 18,19.
Maybe it can´t be helped, after all it's very cheap module.