If the trade is with the Eagles and for picks this year then they need to throw in pick 83 as well for it to be proper value, so 15, 51, 83. Or they could give us 18, 51, 83, 101. Those represent similar value to the 6 pick according to the trade charts (although they aren’t an exact science). We could give them one of our 5ths in either scenario.
I definitely wouldn’t do a trade just for 51. We’d be getting fleeced.