I would not bother attempting to play Watch Dogs with the Intel UHD 620 integrated graphics core. Below are benchmarks for the Intel HD 5500 graphics core in 5th generation Intel Core i series CPUs. Generally speaking, the performance difference between the i5th gen Intel HD 5500 and the 8th gen Intel UHD 620 graphic cores is roughly 20%, but that can vary depending on the specific game.
The Intel HD 5500 is the most current Intel graphics core used to benchmark Watch Dogs. Using the lowest setting at 1024x768 resolution the Intel HD 5500 was able to an average of 17 FPS for the 3 laptops tested. At 20% improvement would mean the Intel UHD 620 can potentially get 20 FPS.