Well, here are some thoughts, even though there is some missing info in the original post.
cash out investor loan @ 4.5% does not sound great, but that depends on some more specifics (LTV, FICO, loan amount, etc).
I just checked an online lender I know of and it looks like they will do a 30 year, 75% LTV, cash out investment (non-owner occupied) conforming loan, for Borrower with a 720+ FICO, @ 3.75% with total estimated fees of $1,919. You can get down to 3.5% with total estimated fees of $3,629. And your rate could be even .125% better with a great FICO of 740+ (3.375% @ $3,294 estimated fees) or better with higher fees. This is as of today.
So, #1 - your deal doesn't sound terrible, but not great either. But, again, that depends on your FICO, loan amount, LTV, etc.
#2) One of the only reasons to do a 15 year loan, is if you just don't want the hassle of paying extra principal on your own - kind of a forced savings account, where you are required to put a certain amount in every month. In other words, you can often get the same or similar "effective" interest rate on a 30 year loan, by just paying additional toward principal every month. But, the 30 year schedule preserves the option to pay the lower 30 year monthly payment, if you want the increased cashflow. I am sure you can find mortgage calculators online to figure that stuff out.
#3) For most loans, you have the option of paying a minimum chunk down and then having the loan "recast" over the remaining term, which will lower your monthly payment. That way, if you decided having the cash out is not doing you any good, and just costing you money, you can just pay the principal down and essentially get back to the original loan amount. But, I think the minimum pay down may be $25k, but you have to check with the specific lender.
#4) 3.5%-4% money is still pretty cheap and I think there should be opportunities to put it to use to make more, but $17k is not a whole lot to put to use on additional properties, in most markets.
#5) There are lenders that will do HELOCs on rental properties. That might be a way you can have the potential to easily and quickly get the cash out if needed, without having to pay for it to sit on the sidelines.