MacBook – Apple Samsung 512 GB SSUBX SSD: Half as fast in MacBook Pro 15“ 2015 than in MBPR 13” 2014

I don't think that this question can be answered with authority.

However, if you are worried about failure due to memory cells wear, we can speculate. Every thing else being equal I would expect the SDD disk to last longer. That's because the SSD controller tends to spread writes among the available memory cells, and the more cells available the less writes each cell will receive.

And of course I would expect a new drive to fail later than an old and used drive.

Then I would say that generaly speaking a newer and bigger SSD will last longer than an older and smaller one.

Is it possible?

Yes.

The question is can you get a drive to upgrade to?

Apple uses a "proprietary PCIe 2.0 x4" interface for their storage. There are SSDs out there that match the specs (like this Samsung on Amazon), but for some reason they are not compatible

So, bottom line....

Yes, you can upgrade it, but only with a genuine Apple SSD (at this point). Your best bet is to get the most you can afford now because there is zero cost savings plus the added headache of disassembly/reassembly. IMO, it just isn't worth it.