Is it possible to execute elliptic curve encryption on small sensor-tags CC2650?
The CC2650 is a Cortex M3 with 128KB flash memory and 20KB SRAM.

This is definitely not enough for RELIC or OpenSSL.

TinyECC fits, but even if this is only for signatures, some symmetric cryptography will be needed in addition to it.

Better options would be Cifra, libhydrogen, tweetNaCl or a minimal BearSSL build. They all fit in about 20 KB flash memory and require little stack to run.