I have the Spurs salary being at $115,000,000, to 14 players for next season with the luxury tax being at almost $121,000,000. Manu retiring would add some breathing room and push that up to around $8.5.
I think Joff opts in and the Spurs pick up Paul.
PATFO seems to really like Forbes, and Bertans, but they are likely to only retain one and that would seem to be Bertans because Forbes, while good, isn't irreplaceable. Bertans isn't either but he has more of a unique skill set.
Parker, Mills, Murray
Green, Manu, Paul, White
Kawhi, Anderson
Aldridge, Gay, Bertans
Gasol, Lauvergne, 1st rounder (hopefully a big)
Thats fifteen spots, 14 if Manu retires.