Unmarked Skillet

I picked this skillet up yesterday . It was caked pretty bad but not warped so I decided to take a chance on it. Seems to be a pretty nice one but being unmarked I was wondering if anyone could give me any information or thoughts on this piece. to the left of the 15 on the bottom looks to be a line I wonder if could be a sort of gate mark or just mold mark. thanks in advance for any help.
https://imgur.com/a/xWcd7

It's a stumper. Physically, it might be initially assumed BSR or Lodge, but none of the markings are consistent with either of those makers. The line in the bottom appears to be just a sand shift in the mold.

Thank you for for your insight. The sand shifting makes sense. I also talked to a collector buddy of mine today he also said the stamps were different and interesting with the 15 being stamped one direction and the 8 the other. It seems to be of high quality with mirror finish. I like it. Wish I knew the age just because that's half the fun.

I'd say that's just 158 and the person who stamped each individual digit (into the aluminum working pattern) wasn't paying attention to the orientation of the 8.