HC-05 connection time problems

Hi all,
we're working with HC-05 and another device (from China, it's called JY-901, and includes three accelerometers and three gyroscopes, plus a bunch of unneeded sensors) that has a bluetooth serial interface (it gives out the raw data of accelerometers via BT).
For energy saving purposes only, we are forced to shut down the JY901 for half an hour and then wake it up for 10 - 15 seconds. We have paired the HC-05 with the JY901 with no problems at all.
But when it comes to connection times there are many problems.
We keep the HC-05 continuously listening (we set up AT+IPSCAN=0,0,0,0 : is it wrong?) and when the JY901 gets back online the connection should start immediately. But that's not always the case: sometimes we can get the HC-05 and JY-901 connected in few seconds (2-3), other times we have a connection time of 15+ seconds, so that we lose the opportunity to read some of the raw data (we need only 256 samples).

How can we solve this problem?
Why does it happen?
What settings to HC-05 do you suggest?