Master Lin states that you are ready for the level II material once you have experienced benefits of the level I meditations.
There is no standard defining moment for moving onto the level II or any other level. My personal experience what more like a drawing towards the level III material, and I had a similar questions. I'm I ready for level III? Have I progressed enough? ... Dispite my conscious mind saying I really wasn't ready, I felt strongly drawn to the material (eventhough I didn't really know what was contained in the material).
Within the year I will take the level IV material, but I'm currently not experiencing a similar pull to it.
There is value to the material, regardless the level and your experience. In the last year I have gone through all of the level I material probably 6 times, the level II material 4 times, and the level III material twice. I also relate SFQ teaching to my other learnings and my daily life.
I also keep reviewing the 6 keys for guidance on how to improve my practice.
Focus on the positive. Use the level II material to help create this better world. By going onto level II you do not give up level I, you just add to it.
You are perfection.
Iam2 
If you