I know this is a late reply Kalvin - but I would place a temporary filter on the hose to the heater for a few months to ensure no more casting sand gets in your new core. But I thought that sand issue was resolved in years earlier than your Jeep.
I was thinking the same thing Barry. As I know it started with my year in 2012. It’s possible it may carried on in 2013 but surprising in 2015. One thing you also have to be careful of is that if you were still using the original MOAT Mopar any freeze you can’t mix it with any other type without the risk of a reaction and it congealing.
When I had to replace my radiator and heater core due to the sand issue I completely flushed the system and went with just a regular good quality antifreeze and it’s been fine ever since.
'12 JK Sport, 5spd ATS auto, P285/70r17 Duratracs on 17x9 Trailmaster steelies, 3" coil-lifted, "DV8" bumpers, Smitty rock rails, K&N w/Magna-flow exh, TrailDash 2’ner, CB, no lockers, Warn VR10, carbon fibre cowl hood, MOAB rating: “billygoat”