Bleep test - shuttle run

Hello, I have a fitness coming up abr wanted to start preparation.

I have been doing cross trainer in the gym as my cardio and weights

I need to achieve level 5.4 on a 15 meter distance bleep test.

I was thinking of starting running outside, I used to do this but it bothers my knees and shins, so I have been doing cross trainer because it's less damage on joints.

Any advice what mile time I should be getting to real 4.5 comfortably?