Airbus defaults the ENG INOP level off altitude to 1500' AGL but leaves the option open for Airlines to use their own level off altitude, that is why you can change it on the PERF page, I have seen it as low as 800' AGL on certain ENG OUT OUT PROC.
The following comes from the Airbus FCTM:
ONE ENGINE INOPERATIVE GO-AROUND
Applicable to: ALL
A one engine inoperative go-around is similar to that flown with all engines. On the application of
TOGA, rudder must be applied promptly to compensate for the increase in thrust and consequently
to keep the beta target centered. Provided the flap lever is selected to Flap 1 or greater, SRS will
engage and will be followed. If SRS is not available, the initial target pitch attitude is 12.5 °. The
lateral FD mode will be GA TRK (or NAV if option installed) and this must be considered with respect
to terrain clearance. ALT should be selected at the engine inoperative acceleration altitude, with
the flap retraction and further climb carried out using the same technique as described in
"ENGINE FAILURE AFTER V1" section.
Here is the reference"ENGINE FAILURE AFTER V1":
ACCELERATION SEGMENT
At the engine-out acceleration altitude, push ALT to level off (or set V/S =0) and allow the speed
to increase. If the aircraft is being flown manually, the PF should remember that, as airspeed
increases, the rudder input needed to keep the beta target centred will reduce. Retract the flaps as normal. When the flap lever is at zero, the beta target reverts to the normal sideslip
indication.
G