Hi there,
OK, Sure I know what you need to change. I did give you a hint, but instead of denying 
you the Thrill of learning something and the journey to obtain the power the knowledge delivers. 
LOL, Left my spoon in the kitchen… Check it
So I G’d the term for you “what parameters affect the response of the BLE connection”
I’ll give you some sample but it’s not rocket science, go read the Links and You’ll know why and what to change (your using all the defaults)
The primary parameters that affect the response of a Bluetooth Low Energy (BLE) connection are the Connection Interval, the Peripheral Latency, and the Supervision Timeout. These parameters are used to balance low power consumption with high data throughput and low latency. The connection interval determines how often the central will ask for data from the peripheral. The lower the slave latency and faster the connection interval, the faster the effective data transfer rate between the peripheral and central.
The best Guide for this is THIS ONE Ultimate Guide to Managing Your BLE Connection | Punch Through.
" The connection interval and slave latency typically affect the performance of a BLE link the most.
HTH
GL 
PJ 