It's not definite that you'll have a shorter draw length, depending on your compound shootin' form, but it's likely. For one thing, you don't have letoff with the longbow. 50 pounds of draw weight at full draw will compress the bones in the wrist, elbow and shoulder joints a lot more than holding 15 pounds with the compound. You won't be stretching into your anchor like you do with the compound. Most people use a more closed stance and lean into the shot when shooting a longbow, as opposed to the open, upright stance most compound shooters use, and that also shortens the draw length.

Another point is the depth of the riser, from the low point in the grip to the back of the bow, is shorter with almost all conventional longbows than it is with most compounds and conventional recurves. AMO draw length is the distance at full draw from the string to the low point of the grip, plus 1.75". Most longbows measure less than 1 3/4" from the low point of the grip to the back of the bow. One can generally use a shorter arrow with the longbow than he can with a recurve. (Can't say that about compounds because most folks are using arrows short enough to pull the arrow point well into the sight window.)

It's hard to make any hard fast rule on that point between recurves and longbows nowadays because there are so many styles and blends of styles with longbows and recurves now. We've got recurves with longbow risers, longbows with recurve risers. Don't know whether to call 'em longcurves or rebows. Anyway, that's why I spoke of conventional recurves and longbows.

Again, a lot depends on your shooting style with the compound more than anything else. For me, my draw length with a compound is 33". With a recurve it's 32". 31" with a longbow.