Haven't heard back from the OP, I think the bickering scared him away.
OP:
Re your question:
"is it possible to upgrade ssd on rmbp 2015?"
Yes, it -IS- "possible", but it won't be cheap and the available solutions aren't the best.
You can buy the OWC replacement, but I understand it runs slower and hotter than the original.
Or, you can look for a -used- Apple-labeled drive on ebay.
Don't expect too good a price, however.
These ARE NOT available "new", at any price.
Really, your best option (in my opinion) is to become more critical of what you keep on the MacBook you have now, and "get rid of the excess".
If you need to carry some "additional stuff" around with you, get a pre-packaged USB3 external SSD, something like this:
http://www.amazon.com/exec/obidos/ASIN/B00ZTRY532?tag=delt-20
...and plug it in when needed.
Unfortunately, this is the trend now with Apple.
Storage is no longer [easily] upgradeable.
If you're going to need "more storage" over the long run, you've got to "pay Apple's price" up front at original purchase time.
Well considering he just created an account he probably doesn't really visit this forum often. This is fairly typical.
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