Equilibration of new lipid model

GROMACS version: 2021.4
GROMACS modification: Yes/No
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I used the CGenFF tool to model a PEGylated lipid.
Afterward, I placed the resulting PDB file in SPC water and performed a 2 ns Berendsen and a 50 ns Parrinello-Rahman simulation.
I would now like to evaluate whether the generated model has been stabilized.
What criteria should I use to assess its stability?

Thank you