It is under APP for another 1 yr 3 months. 16gb ram but downside is that it has only 1tb hdd storage. will need to explore how best to deploy SSD without voiding warranty
Easy.
a)The only way to maintain AppleCare is to start from external and, when AppleCare is up, install inside. It's more expensive this way but AppleCare remains intact. An SSD in a Thunderbolt 2 dock is pretty fast but not as fast as...
b) Screw AppleCare and throw an SSD inside now. There are two busses: A PCIe 3x4 2TB SSD is $600 + Labor (an hour) and is roughly 6x faster than a SATA III SSD — 2TB is $350 for parts plus that same hour labor (250G – 4TB available). You can install both, actually as long as it's a 27" iMac.
Yes, 6TB SSD internal storage is possible — $1,400 for the parts and about one hour labor. BTW, if I found a 2015 i7 for $1,100 or so, this is what I would do, AppleCare or not.