Assume you have a very long input file with no syntax errors.
It is clear for this case that the time to completion is what is important.
Assume you have a very long input file with no syntax errors except at the very end of the file. (syntax test program).
What is more important? Time to completion with error message or correctly identifying line and statement in program?
Note, these require different strategies for different requirements.
If the requirements for the interpreter are for checking syntax errors then time to find and report error is important.
If the requirements for the interpreter are for running presumably error free code then time to complete error free code is much more important than time to detect and report syntax errors.