Maybe I'm missing something, but you said you can "leave it" and it will earn 2.5% interest. If it truly is a $225K balance, that leaves you short of $400K by the time you are 62 - again, assuming it's a $225K balance now and earns 2.5% annually.
OR you can take $225K and invest it - even if it's just 7% over the next 23 years you'll have $1 MILLION. Even if you go conservatively and use 6% average ROI, you'd end up with ~$860K by the time you are 62.
The annual benefit at 62, if you leave it in the pension, is $26,400. If it really is a $225K balance right now and you start drawing down at age 62 while it continues to earn 2.5%, they project you to die/stop withdrawing around age 82 (just plugging in the math there and when you'd go negative).
Now let's jump back to the IRA that you've conservatively invested and received 6% ROI annually for 23 years. You're sitting at $860K there at age 62 and that's not even counting your other investments. You can withdraw almost $35K/year and assuming a 4% ROI you'd never run out of your stash in that IRA.
I think you should definitely go with rolling it into an IRA. Even conservatively at 6% ROI the next 23 years, you'll definitely be able to beat out the $2,200 monthly pension. Some other factors are in play - what would you like your survivorship plans to be, do you have genetic or other health factors that would significantly reduce your expected life, etc.
Assuming I keep the annuity, how do I determine how much I need to FIRE?
Depends on your expenses. If you do keep it in the pension and ignore my advice above, you'll have an annual benefit of $26,400 - but only starting at age 62. The rest of your stash is ~$290K, nearly all taxable. If you move all that into an AA that yields 4% annually, you can withdraw ~$20K/year and it will run out when you turn 62.
If you combine the $225K and the $290K, you're looking at 4% being just north of $20K annually...and a stash that should last you the rest of your life if your annual expenses are $20K.
So a lot of factors - are you planning on continuing to work somewhere else in the near future? Side gig? Etc. Any major factors that would indicate you won't live past 80-85? Do you want to leave a stash for any mini-mustaches, etc.?