I see that you're using gen_private_key. This generates arbitrary secure random private keys, using urandom. urandom might be slow depending on your system - do you really need it? I assume whatever you're doing (brute force search?) will generate the private keys in some other fashion, so you can just set prvkey_dec to an integer representing the private key directly.

I also see that iceland2k14/secp256k1 does not provide the source for its libraries which is a bit concerning.