The 30L15 is a low impedance high gain double triode. The low voltage high current suggests a low noise design, used in the front end stages in a television tuner.
The other 30L15 in the museum has a different construction. This one has a perforated outer screen as well as an inter-section screening plate.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 47 mm tall.
References: Data-sheet & 1040. Type 30L15 was first introduced in 1960. See also 1960 adverts.