Reverse a linked list
Test cases right off the bat are a good sign. You only have one, but it is now easier to expand other conditions. I like to add in conditions for list has 0 elements and list is null. You'll be able to prove that those work, or if they don't work, prove that changing it didn't break anything.

Two of the methods use the word Reserve instead of Reverse: ReservseLinkedListTest and Reserve.

For a 15 minute code interview, I'd give it a passing grade.