I think the 1521 may pull more amps than a XL motor, maybe someone with both can chime in on this. I know my 1515 2.5D pulls about as many amps as my 10XL (similar kv).
This is a big difference. If you don't change your gearing accordingly, the 1521 will pull more amps. The 1521 1D is rated at 200A for 30sec max (3000W). On 4s it could pull even more Amps. But it really depends on your gearing and how good your lipos are able to hold their voltage. With your desired setup your ESC would be the weakest link. I guess your lipo is able to handle more than 100A burst.
The Neu 1521/1.5D (1860kv) seems to be more appropriate. It's rated for 90A. But could easely pull more Amps on 4s depending on your gearing, lipos, driving style and so many more factors.
A Neu 1515 should suffice for an Emaxx. But the MM will always be your limiting factor when you want to gear up (or maybe your lipos).