Speaking VGA-->VGA (HD15 to HD15), you should be fine up to 20-25' or so. I don't think HD15 --> BNC really changes anything, just the termination, if that's your situation.
You're totally in fair territory for VGA. Beyond 20-25' or so, you'd consider using an in-line amp. I wouldn't be concerned.
You're totally in fair territory for VGA. Beyond 20-25' or so, you'd consider using an in-line amp. I wouldn't be concerned.