Installment loan "utilization" isn't calculated in the same way as revolving utilization. It's mostly if not completely ignored by FICO actually.
If we're just talking FICO scoring, you're better off keeping your existing tradeline for as long as possible; if you need the payment to be reduced for whatever reason, then you might consider kicking additional money to it and refinancing. Or if you're trying to make room for a DTI calculation may be similar.
Refinancing should always come down to a financial decision anyway. Generally speaking it'll always be a negative for FICO.