BIAB with a Keggle

Starting to do BIAB, 15.5 Keggle too big or just right????

Errr...
Yes...
No...
Maybe...

In all seriousness, way more details please:
Batch size
APV range you would like the capability for
http://www.brewersfriend.com/mash/ if you dont know above question
Burner type

IMHO, a keggle is perfect for 5 or 10 gallon batches. I mash in one and boil in another and they work great. The only drawback is they hold their heat forever and until I can afford to upgrade my cooling system it takes a while to chill to pitching.

I did a four-five gallon batch (meant to be 5 but I underestimated absorption/evaporation, and then didn't bother to add top-off water to the fermenter) BIAB in my 15.5 gal keggle with no issues. I use a propane burner that used to be for making big batches of tomato sauce. I did make a wind blocker for it. I don't remember the weight of my grain bill, but the beer came out to 8% abv.

Sorry for the lack of info...

5 gal batches
Mainly only brewing brown ales and Wheat never really did anything heavy
Burner type=ole turkey fryer

Just want to make sure this is not an over kill

For 5 gallon it is a bit overkill, unless you were planning on occasionally brewing big apv beers.
It is certainly fine to use it, but because of the larger size and extra mass of stainless it will use way more propane (and then more water/time to chill at the end) to do the same job than a 7 - 10 gallon pot would!

It's what I use for 5 gal BIAB...
I like to go for a 6 gallon batch, and by the time I get rid of almost a gallon of trub and gunk, it works out to be just about right for filling a corny, so working backwards:
6 gallon batch
2 gallons boil off
.75 to 1 gal grain absorption
= almost 9 gallons plus grain at dough-in
That puts your keggle at about 2/3 full... just right.

I find the heat-sink of the keggle an advantage. I suggest resisting the urge to bring up the temp during the mash though. It will continue to rise after flame-out. If you must, give it a 10-second blast, and wait a bit before giving it another one.

I also use a keggle for BIAB. When I'm doing my typical 5 gallon batches, I add 8gallons for strike volume. I usually start my boil with a preboil volume of 7 gallons. I did a 10 gallon batch and almost maxed it out for mashing. Had to mash thicker and sparge a little over the grains. The 10 gal batch was a pain in the butt and it was only a 1.050 OG amber ale. I don't think I care to do many more 10 gal batches until I rig up a pulley system.

Good stuff, then its settled, i will be having my keggle made, just got a keg, going to have my father in law cut the top with his plasma cutter, sent my grandma my measurments for a voile bag, now as soon as i get back from the stan ill be on my way to AG.

I'm also doing BIAB in a keggle. ~8 gallons strike water, 7 gallons boil, 5.5 gallons into the fermenter, 5 gallons into the corner/bottles.

Works perfectly. Its nice, because I don't have to worry about boilovers (at least for 5gal batches). I still use fermcap-s, but that's just more for peace of mind than an absolute need.