A 15 page document to justify a $40K simplified acquisition does appear to contradict the concept of "simplified acquisition." It's not clear how the limitations on the use of LPTA for certain DOD acquisitions would affect the use of FAR Part 13 procedures, since not being able to use the LPTA method in FAR Part 15 simply means the trade-off method in Part 15 should be used instead. Nevertheless, if an acquisition qualifies for the use of FAR Part 13, the procedures in FAR Subpart 13.1 apply. Note one of those procedures at FAR 13.106-3(b): "Keep documentation to a minimum." The documentation requirement for actions awarded iaw FAR Subpart 13.5 is a bit more detailed (see FAR 13.501). However, to many experienced contracting professionals, this would suggest something in the neighborhood of 1-3 pages of documentation to sufficiently address the issues mentioned in FAR 13.106-3 and/or 13.501. The best source selection guides to use for FAR Part 13 buys are simply FAR Part 13 and DFARS Part 213. You should also consult your own agency's FAR supplement to check for any additional requirements.