No ! Comments do not effect execution speed of a program. Particularly in C#, comments are not parsed to the compiler. They are eliminated in the lexical analysis.
But, do not keep commented files which are not necessary. The main purpose of comment should be document your code. Although, it has nothing to with the performance of your application/program.
You can check this is using
IL Disassembler[
^].
I hope it was helpful and incase any further clarification required on this topic please reply :)