You are asking about L2ARC yet you haven’t posted any plain, ARC statistics? ARC and L2ARC are all about repeated reads on your system.
Start with the basics to understand ZFS and how it uses memory. If you just want to add in L2ARC and play with it, go ahead. You can remove it from your system without damaging your pools.
BASICS
iX Systems pool layout whitepaper
Special VDEV (sVDEV) Planning, Sizing, and Considerations
