According to this snippet i found on the web it would suggest pre 80’s.
“Sometimes you can easily determine which decade the tire belongs in based on the sizing nomenclature, brand or style. Let's say you're looking at an LR78-15 tire, using the same 306 date code we mentioned earlier. Based on the alpha-numeric sizing nomenclature, it would be our best guess that the tire was manufactured in 1976, as the now standard P metric sizing (ex. P215/75R15) became more popular in the 1980's. You could also expect this tire to be missing the standardized safety warnings on the sidewall and any type of tread wear indicators, as those features were mandated later than 1976. That's just one example but you can see how certain styles or sizes can be quickly identified by decade.“