2.5" Drop is alot for springs. Your shocks would probably last for 1 year depending on its condition now.
It would also be very noisy when you go over bumps. As your shocks will bottom out since it doesn't have much travel.
If you're on stock height now and it rubs. You will be lucky to be able to turn your wheel on a 2.5" drop with 245/45 tyres.
I would personally skip the springs and get smaller tyres. Worst case, You install your springs and the car is stuck and cant move because of your tyres.
I had 215/45 on 17x8+32 with 1.5" drop srpings and my car couldnt turn. Going straight was almost a mission. The slightest bump and the guards would smash against the tyre.
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