Hi,
I just bought exactly the same bike. Would like to increase the speed limit from 15mph/25kmh to 20mph/30kmh.
I heard that there is a cable for sale what you can connect to the motor and adjust this limit. (www.aliexpress.com)
There is a guide how to do this with the same manufacture but with a different model. (https://electricbike-blog.com/2015/06/26/a-hackers-guide-to-programming-the-bbs02/)
I have no idea if it will work with the crosscity motor as pinout of the socked could be different.
Any ideas guys?