IPhone 6s Plus sim locked

Ok so I have an iPhone 5s for sprint and it broke so I bought a iPhone 6s Plus for sprint on Craigslist and when I put my SIM card in I have from my iPhone 5s it connects with LTE and internet but after about 2 minutes it says "Sim locked please power cycle" and I did that and if still doesn't work, I can't even call or text.

Yes

Sorry it's not gonna work like that. You gotta get a new sim car for the iPhone 6S and then ask sprint to transfer the service and number over to the new sim