Stay w/ a 15 yr @ 2.75%, or go to a 30 yr and take the cash?

[Jonathan Watson]

Just looking for a little advice/insight into how best to approach my mortgage.

Current Situation...

I have 15yr fixed on my primary res. with 14 yrs left.  I owe about $225k on it still (home is worth about $485k). Interest rate is 2.75%.  Payment (not taxes/ins) is $1640 (paying $1100 of principal every month).

I also have a HELOC (currently at 4.75%) for $125k (remaining balance of $45k was used to purchase 2 out-of-state investment properties, cash-flowing about $400/mo after mortgage, insurance, taxes, HELOC payment).

Should I...?

Refinance into a 30 yr fixed, with a monthly payment of about $1050.  I would pay down the principal about $350/mo.  I would gain an additional $600 of cash every month which I'd like to use to store up for future investments

Should I refinance and take the $600 additional monthly liquidity for future investments and thus lose the amazing 2.75% interest rate...?

What would you do?