Briefly, that's a big jump in size. 56cm would be for someone around 5'10", 61cm for someone 6'2" (very, very roughly).
Ultimately, frame sizes come down to stack and reach. They don't always increase consistently with nominal frame size (depends on manufacturer), but a 61cm frame will generally be a lot bigger in both. Attempting to overcome that through a shorter stem will lead to odd handling.
Also keep in mind standover height. I'm 6'3 and can barely stand over my 60cm frame. This is not a huge deal for me since it's my road bike, but I can imagine this would get annoying real quick in a city setting.
Briefly, that's a big jump in size. 56cm would be for someone around 5'10", 61cm for someone 6'2" (very, very roughly).
Ultimately, frame sizes come down to stack and reach. They don't always increase consistently with nominal frame size (depends on manufacturer), but a 61cm frame will generally be a lot bigger in both. Attempting to overcome that through a shorter stem will lead to odd handling.