The 115 is the 9/0 Penn Senator, the big-game size of the star-drag reel Penn introduced in 1936. In the Senator numbering, 113 is 4/0, 114 is 6/0, 115 is 9/0 and 116 is 12/0, and an L marks the wide-spool version.
A 9/0 is overkill for most anglers; it is built for giant bluefin, big sharks and heavy bottom fishing from a boat, on a stout rod in a harness or rod holder. Like the smaller Senators it is simple inside and Penn still supplies parts, so even a hard-fished reel can be rebuilt.
Our latest snapshot found about 35 complete 9/0 Senators, mostly at $110 to $180 delivered. These reels are heavy, and shipping often adds $15 to $30, so compare delivered totals rather than item prices.
The same snapshot found several listings sharing word-for-word titles across different sellers, a copied-listing warning sign, so stick to sellers with a track record. The catalogue files it under the 1940s, the earliest decade it lists; the Senator design dates from 1936.