If you are coming from Overwatch and want to have the same sensitivity in VALORANT, you cannot simply use the same sensitivity. The games use different settings, and therefore sensitivity will not be the same in the two games.
Luckily, calculating your VALORANT sensitivity from your current Overwatch sensitivity is super easy.
To convert your Overwatch sensitivity to the same sensitivity in VALORANT, you will just have to divide your Overwatch sens. with 10.6.
Overwatch sensitivity / 10.6 = VALORANT sensitivity
You have your Overwatch sensitivity set to 15. If you want the sensitivity to feel the same in VALORANT, you want to set it to:
15 / 10.6 = 1.4