Try syncing enough music to fill it anyway. The "other" space might shrink as you put media on it. If it doesn't and tells you that you're full, then it's time for a restore.
A restore really isn't that bad. Just sync your phone first to make a backup, then restore from that backup. The whole process takes about 10 minutes max (minus reloading your media, which you don't have right now anyway)
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