To estimate the price of the 2023 Lexus LS350 V6 3.5L Excellence (Top) with 15500 km mileage, I considered the listed prices of similar cars. The 2021 model with only 1000 km is listed at SAR 306,000, and the 2022 model with 55,000 km is listed at SAR 298,500. The 2023 model has lower mileage than the 2022 model, which suggests it should be priced higher than SAR 298,500. However, it is newer than the 2021 model, which is listed at SAR 306,000, but with significantly more mileage. Considering these factors, the estimated price should be slightly below the 2021 model's listing due to the higher mileage but above the 2022 model's listing due to being a newer model with less mileage.