What are the dimensions of your 150? I havn't seen a 150 that could house a jardini with any tankmates when full grown.
And just because an irresponsible person keeps an aro in a 55 gallon doesn't mean that its ok for you to put it in something a little bigger than that, but still not the minimum requirement for the fish. It is similar to saying, "That guy is murdering 6 people, I am only going to murder 2." Just because someone else does something wrong doesn't mean you just have to be just a bit better than them.
And if you want tankmates with the reticulated ray, then you can get...Just don't get a reticulated ray. If you want "big mean fish" for your 150 then just get some piranhas.