First investment property advice needed

[Chase Brelsford]

I've purchased a second home (investment property). The current rate for 15 year mortgage they're offering me is 3.875, with 20% down on a 70,000 home. The closing costs are 3,000 which is to high i think. Are the closing costs negotiable? I'm not happy with the interest rate either. Their reasoning is credit score. Out of the 3 credit company's they use, 1 shows me having mid 700's, the other 2 show high 600's because of medical bills on them. Can I pay down more to drop the interest rate? Would a co signer drop interest rate? Also am I better off with a 30 year instead of a 15 year? Any advice is appreciated.