Why John Tukey set 1.5 IQR to detect outliers instead of 1 or 2? To define outliers, why we cannot use:
Lower Limit: Q1-1xIQR
Upper Limit: Q3+1xIQR
OR
Lower Limit: Q1-2xIQR
Upper Limit: Q3+2xIQR

We certainly CAN use whatever outlier bound we wish to use, but we will have to justify it eventually.  In the not-so-recent past, it was typical to expect distributions to be Gaussian.  With that assumption, ±1IQR is too exclusive, resulting in too MANY outliers, ±2IQR is too inclusive, resulting in too FEW outliers.  ±1.5IQR is easy to remember, and is a reasonable compromise, under assumptions of Gaussianity.
However, for your distribution and expected outlier fraction, those assumptions may not be appropriate.  Additionally, perhaps the definition of outlier is incorrect for your problem, and requires greater detail than just how it behaves within the bounds of a single metric?
