It’s faster only if the structure is extremely slow to copy. In this case, FVector is a mere 12 bytes, and it may well be faster to put it on the stack just to avoid cache misses.
More practically, the bottleneck for actor collisions is never going to be the cost of passing an FVector. Across all games written in UE4, for the entire history of the human race, the total CPU time spent copying that FVector will be less than the time I spent writing this response.