Here is the plain English:
Section 8 on a renewal is for someone who did not use the mark “in commerce”.
Section 9 on a renewal is for someone who DID use the mark “in commerce” (this would be you).
Mod edit: Please see @packetfire correction below.
Section 15 is an extra add-on to obtain “incontestability”, which is a very good thing to point to both in threatening letters to infringers, and in court if someone has to be sued, as it makes it much harder to contest the validity of the trademark.
To explain, every infringer will invariably claim that the copyright or trademark is somehow invalid or was obtained by fraud, as it is an attempt to put the plaintiff on “the defensive”. “Incontestability” creates a presumption that the Court will respect that the specific trademark given section 15 treatment is valid and cannot be challenged. This MOSTLY works.