I know I'm late to this discussion, based on the request for quick replies, but $150 sounds like a lot. Would a 15-91 have been sold in a treadle table without the treadle metal?. If you're using it for sewing, I wouldn't pay that. If you're wanting to display it in your living room, maybe, because the table appears to be in nice condition.
Interestingly I saw a news piece last night about a Ugandan refugee camp in which a young girl was using what looked to be a 15 in a treadle table; I would guess it doesn't get a lot of maintenance. The news story was interesting in itself but I will admit I was distracted by the machine.