I would like to comment on behalf of the Developer Advisory board with the goal of making the WHY of this proposal clear to governance.
Summary for upgrade 15 isthmus hardfork:
There are three parts of this change. The first is that this hard fork implements the ethereum Prague hardfork changes which include a number of EIPs. The second change is that the operator fee outlined in the previous proposal will go live. The third is that the L2 withdrawals root is put in the block header. This makes it easier for chain participants to inspect or and verify the correct output root. Prior to this change, in order to verify the output root individuals would need to run an archival node, but with this change we put the withdrawal root readily available in the block header, which any full node can provide. This enables third parties to compute block commitment outputs without grabbing the withdrawal root from an archival node.