I have the wot and it almost never comes off of my detector. Some say it's too big for general detecting and it can be frustrating at first but I love it.
Unless you have a lot of practice using a dd coil I wouldn't try one. If you know how to work a dd coil though and go slow and listen for tones it's great.
I run my safari in all metal ferrous saved to conductive so all iron sounds low and keepers give high tone. Saving ferrous to conductive will give you icons also, which I like just to establish what range signals are in, I don't like using and memorizing numerical read outs. If you want deep oldies for my area I just ignore all signals shallower than 6 inches.
Running nearly same settings my buddy on his se pro with stock coil either cannot hear some of the really deep targets I find or they sound/display as iron. The stock pro coil is good, I,m not saying it's bad at all it's just that the wot is much deeper.
If your soil is too mineralized a larger coil is not supposed to increase your depth because it takes in too much ground matrix. Weird thing is the soil here is awful and my wot is uneffected. Just remember to swing very slow.
Only downside is its heavy...I run a harness with mine. Don't need to for couple hour hunt but with harness I can go all day with no fatigue. I have Sunray probe mounted on mine also.
Sorry I haven't tried the nel coil 15 but have used other nel coils before and like them.
Wot,s are spendy new but you can pick up used one for about 120 and they resale we'll.
Hop this helps,
Dave