OOF-dah.  Technically, I think you can do it with the engine in the truck, but I think you will find it to be extremely difficult, with poor visualization and cramped spaces.  Doing it on an engine stand might be easier, even with the added work to get the engine out.  I have even heard of some people taking the cab off, though that's more of a pro-shop move.

Not to frost your cookies or anything, but are you sure you want to tackle this job?  I mean, we aren't talking some old GM small block or Ford flathead; the ecodiesel is a very complicated and fussy engine.  If there ever was a DIY job that was fraught with peril, this is it.  If you are up to it, then more power to you.  But you need to do all the homework before you start.  You will not only need the Ram 1500 shop manual, but probably the ecodiesel  book, too.

I would hate for you to be 40-hours into the project, only to realize you have to get it towed to get a new motor installed.  I seriously don't want to discourage you and sincerely hope you do it and succeed.  But still, OOF-dah.

Posted by: @9191

Can head gaskets on 2015 ram ecodiesel 3.0 two wheel drive be replaced with motor left in the vehicle, me and grandson getting ready to tackle, any heads up and information will be greatly appreciated

Changing head gaskets isn't really for the faint of heart DIYer. Pretty much the entire top of the engine needs taken apart, and you need a torque wrench, following precisely along with a maintenance manual, both during disassembly and reassembly.  I couldn't find anything on Amazon regarding the EcoDiesel, all I could find was the Haynes with the Cummins.

Have you verified the head gasket is indeed leaking? The make a special tool to check for head gasket leaks. 

probably not, but if you don't know what you're doing I urge you to print the procedure from a service manual. Going freestyle is just asking for problems. There are procedure that must be followed exactly if you don't want to be doing the job all over again.