tune isnt gonna bring the turbo on song any quicker... exhaust flow governs how quickly ur turbo comes onto boost..
first thing u should look @ is exhaust flow properties. check ur cat, make sure nothings block and ur exhaust is as free flowing as possible.. check wastegate operation as thats what controls the speed of the turbine. if its opening a lil too early and slow enough, it will make ur turbo laggier than it should be. spring tension is something to check for on the gate.
2ndly cams with more duration and lift will bring the turbo onto song quicker, but ull need supporting mods.
If its an aftermarket manifold, wrap it up. heat = energy. the more heat u can keep inside the exhaust the more energy will be exerted to the turbine wheel at a higher velocity hence reduce lag.
check ur intake for restriction.. try blowing through a kfc straw or sucking.. not very good for flow compared to something bigger like a maccas straw.
a tune will only make what u have a lil more drivable.. but it wont bring ur turbo on full song any quicker.
START WITH THE WASTEGATE SPRING TENSION FIRST