Your numbers show a difference of $208.06/mo in PI payments. If your the total payment change you used in your calculation included the change due to dropping TI escrow payments, you failed to account for making those payments in your calculated return. Using cash flow analysis, I don't see an actual gain. You spent an extra $3612 at the start followed by 180 months of $208.06 to save $656.22 for the 170 months at the end of the cash flow. The IRR function returns an error for this cash flow.

You’re only looking at cash. On the equity side, I went from gaining $157.50 equity per month to gaining $532.59/mo and this difference will only widen as the loan amortizes. This is why the loan will be paid off in 15y instead of 30. The refi does involve a higher payment, a transfer of wealth from my cash account to my equity account, but I’m good with that because I’m mostly interested in net worth.

The increased payment size only partially offsets the increased rate of principal gain as shown under the “Savings” heading.

I suppose to be extra fair, I could have deducted from cash flows the implied interest I could have earned in similarly risk-free investments with the extra $178.90 per month and $3612 closing costs. At a 2% “cost of capital” this drops ROI to about 10.8%. This is still a very respectable return for a zero risk investment. If I were comparing this investment to, for example, the alternative of a junk bond, I would have to use the originally calculated return of 14% because I would need nominally that much return from the bond to end up with the same amount of money in the end.

One could go further down the rabbit hole with inflation adjustments, yearly amortization charts, compounding, and taxes, but most of these factors lean in favor of the refi anyway.

I excluded any escrow info from all numbers, because that doesn’t change anyway.