A Lenovo thinkpad p71 is 17.3"
The specs on the bag say 16 in (40.6 cm) laptop pocket for 15 (38.1 cm) in laptops
So no, it won't fit.
The maximum dimensions of the bag is 21.4" by specifications given in details. A Lenovo P71 is 19.7", it might barely fit if you just shove it in the main compartment somewhere rather than in the protective pocket.