D10 is not needed, T15 could take over its national transponders at any time and it hasn't served spot beams for years.
D8 was launched well before these satellites and when they renewed its license Directv reported to the FCC it has fuel life until 2034.
None of those satellites are beyond their design life, perhaps you ought to review the math you used to add "15" to the year they were launched. When Directv has to renew their licenses hopefully they will include something in the request about their fuel life, but saying that D11 and beyond will last until 2030 is only assuming about 5 or 6 years beyond the design life.
Pretty much everything lasts longer than 5 or 6 years beyond the design life. Hell, D4S and D5 were launched almost 20 years ago with a 10 year design life and they are still up there (while D5 currently isn't being used for anything since the 110 location has been phased out, I think D4S still serves some of the MPEG2 SD spot beams at 101)