Why does the F-15 have a swept-back trailing edge at its wing tips? The F-15's wing has an curious feature: a swept-back trailing edge near the wingtips, along with an unswept inboard portion of the wing.



(Modified from https://en.wikipedia.org/wiki/McDonnell_Douglas_F-15_Eagle)

This feature is not present on comparable teen-series fighters (e.g. the F-16):



(https://en.wikipedia.org/wiki/General_Dynamics_F-16_Fighting_Falcon)

Lots of Soviet-made aircraft (e.g. MiG-25, -29, and Su-27 families) appear to use a swept trailing edge. However, these fighters all have a constant sweep across the wing--not two sections of different sweep like the F-15.


(https://en.wikipedia.org/wiki/Sukhoi_Su-27)

Why then does the F-15 have such a seemingly unique feature (i.e. a trailing edge with two sections of differing sweep)? Clearly its designers must have thought it served some purpose--I presume they would not have added it for mere decoration.

EDIT: to clarify, my question seeks the physical reason(s) for why the trailing edge of the wing tip has a rearward sweep--not why the wings are cropped at an oblique angle, or a citation of historical precedent.

EDIT 2: I'd also like a well-sourced answer, if possible.
The F-15 wingtip is a "raked" tip configuration, which increases lift and decreases drag.1
[]2

This is the design decided by the USAF after discovery of several design deficiencies during initial flight test which included aeroelastic deficiencies (wing bending) and aerodynamic effects (buffeting). "In early June 1974, the Air Force flew the “raked” tip configuration and were completely satisfied
with the configuration’s buffet characteristics."  The Saga of the F-15 Wingtip