if you are using 1.3 ecu then your system is going to be lean means less fuel more air and timing difference will also occur.
u should also chek for injectors whether they are usable for 1.5 or not . if injector size is smaller then less fuel will b injected.
best solution try to find pakistani city 1.5 ecu that came in my city 99 1.5 . its model is P3S-K01 if you find different ecu with the same pinout and harness it can also be an easy ecu swap. wiring is same everything is same just it is designed for 1.5 .
i also swapped engine from 1.5 to 1.4 and problem was occuring just fuel mileage decrease fron 18km/l to 12km/l on highway