This is a tough one, and I wish you well on your situation/burn out. Just to make sure I understand, if you keep working at this same company for 2.5 years, how much money are we talking? Either real dollars or as a percentage of your FIRE goal? I'd hate to walk away from that money, given how much you've already personally invested. Of course, your health & wellness comes first, so if there's no way to manage your current workload & position while staying healthy, I think you should look for another role. Sometimes larger companies will "buy you out" of your options, by offering you a similar vesting schedule at their company. YMMV.
If you are already facing a low performance review, you may not be in the strongest negotiating position. But, have you already been working with your manager to be clear on expectations, support, prioritization, etc? Is he/she aware & supportive of you generally? That would also modify my position.