Looks like you have a Jensen 15" in there (P15LL?)...if it is, you can verify the manufacture date:
"All Jensen speakers also include a date and manufacturer's code. Jensen's source code is 220. Accompanying the company specific ( EIA ) code (220) is the last digit of the year and the 2 digits of the week manufactured, creating a 6 digit code usually imprinted on the speaker edge or the magnet housing. "