I have the large D800 which is has the 15.4 inch as well, I have an Ogio Metro which it fits in fine with PLENTY of room for book and other things:
Its pricey but you can find coupons for ebags everywhere i think I paid 48 or so..
I just got this one:
for my M140 it fits well I think the D800 will fit but I haven't tested yet.
I also tried to look for bags that...