Trading a #3 overall pick for something between 10 and 20 in terms of pick order is stupid. There's underlying issues. No team makes a calculated drop from 3 to 15, thats absurd.
That was my initial thought as well.
OTOH, if you look at a lot of the starting RBs around the NFL, there aren't many that were 1st round picks. Basically, using a first for a RB is stupid - you don't have to "pay" that high of a price for a good one. So, if you're the new GM in Cleveland and in looking at the current roster you determine the cupboard is pretty bare, recouping a 1st for the previous regime's poor decision isn't terrible. And if you never liked Richardson or don't think he will be the type of player that will play to the level of a first rounder, no matter where he was taken in the 1st, why not trade him now when you can still get a first? Now, if needed, you'll have 2 firsts to grab a franchise QB in the next draft (b/c Weeden ain't one).
Is there anyone else on the roster they could have got a first for (factoring in age, trouble history and contract)?