Mortgage Refinance Question

[MoneyQuestions4U]

Hello!  I'm hoping to get some advice on a refinance.

We closed on our house November 1, 2018, put 20% down.  Rates were very high at the time, so we paid 4.875% for a 30 year mortgage.  In the meantime, we have paid 21% of the principal off, been able to do this since we only borrowed about 40% of our max loan approval amount and watch what we spend. 

We still max out 401k and ROTH IRA. 

I am HOPING to pay this off in 4-7 years, we are likely to upgrade a bit to a new home once this is paid off, but we could stay too.

The lender gave me the following rates:
Fixed 15 Year Conventional Rate term Refinance

3.250%....$3,989 to close.
3.375%....$3,405 to close
3.500%....$2,645to close.

How do those closing figures look to you?  I'm leaning towards the 3.5%. 

Anything I should be aware of when refinancing?  This would be the first time I would do a refi.

[A Fella from Stella]

Since you are paying it off so fast, what is the total savings you'll see in the roughly 1% rate reduction?

This would make perfect sense if you were going to need more time to pay it off. For example, I have a rate like yours on a 30 year, then re-financed to 3%, a rate I paid extra to get, on a 15 year loan. It will take me 10-12 years to pay this loan off, so the savings is significant.