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15% isn't crazy for short money like this if that's an annual rate, on $30k it's roughly $375 a month in interest, so the real question is how fast you can finish and get out. Before you take anyone's money, read your current note for a due on encumbrance clause. Most hard money first liens don't allow a second lien without written consent, so ask your current lender first if they'll fund the extra $30k as an additional draw. At $120k total against a $320k ARV you've got plenty of room, and a cash out refi once it's done would pay off both cleanly.