I looked in the LISP 1.5 Programmer's Manual (1965) and found a reference to "comment":
Overlord direction cards are punched in Share symbolic format; the direction starts
in column 8, and the comments field starts in column 16. Some Overlord cards will
now be described.
"Overlord" appears to refer to a tape control language, which would not strictly be considered as part of the file contents (which is the LISP program code).
A complete sample program starts with the header
* M948-1207 LEVIN, LISP, TEST, 2,3,250,0
TEST WANG ALGORITHM FOR THE PROPOSITIONAL CALCULUS
This header appears to be repeated verbatim in the output. The header syntax does not appear to conform to LISP syntax, so it probably shouldn't be considered a "LISP comment", but rather is probably useful for an operator to sort out which output belongs to which program.
The ability to use
; to introduce comments in LISP source code appears to have evolved later than 1.5.