A blockchain cryptography expert is someone who specializes in the field of blockchain technology and cryptography. They have in-depth knowledge and expertise in the cryptographic principles and algorithms used in blockchain systems. As for the 15 features/advantages of such a person, here are some:

1. Strong understanding of cryptographic algorithms and protocols.

2. Ability to design and implement secure blockchain systems.

3. Expertise in key management and secure key exchange.

4. Knowledge of secure hashing algorithms.

5. Understanding of digital signatures and their applications in blockchain.

6. Proficiency in encryption and decryption techniques.

7. Ability to analyze and identify vulnerabilities in blockchain systems.

8. Knowledge of secure consensus mechanisms.

9. Familiarity with privacy-enhancing techniques in blockchain.

10. Understanding of secure multi-party computation.

11. Expertise in secure smart contract development.

12. Knowledge of secure data storage and retrieval in blockchain.

13. Ability to design and implement secure authentication mechanisms.

14. Proficiency in secure transaction verification and validation.

15. Understanding of secure blockchain network architecture.

Please note that these are just some of the features and advantages that a blockchain cryptography expert may possess. The field is constantly evolving, and there may be additional skills and knowledge required depending on the specific context and advancements in the industry.