What should be done with 15 Riyals found in a shopping mall, and is taking this amount considered a sin, knowing the difficulty of identifying its owner, and do the rulings of "Luqata" (found property) apply to it?

A small find (Luqatah) that the owner is not particularly concerned about may be taken and utilized without any disagreement among the scholars. The definition of "small" (Yaseer) is determined by common practice, and this varies with time and place. If the amount is considered small عرفاً (by common custom), then it is permissible to take possession of it. Otherwise, it must be announced for a year. If the owner is not found, then it is permissible to take possession of it, with the guarantee of returning it to its owner if he appears.