Possibly. Don't know much about the US history on registered mail (bigger brains here can fill you in) but in Canada registered mail started out as Money Letters, which were exactly what they sound like. You would pay an extra fee to ensure money enclosed in the letter was tracked and made sure it got to it's destination. They actually wrote Money Letter on the front of the letter to indicate what it was.
The Canadian Registered mail system was also introduced in April of 1855. Handstamps which read REGISTERED replaced MONEY LETTER on the front of the letter.
You still don't have a Scott 163. As the date of usage is 1871 the stamp should be a Scott 152 as Scott 163 was not issued until 1873. There is a slim, but possible chance your 15c stamp is grilled. You should check the 3c stamps for grills as well.