Spurs can pretty easily get to 15M in cap space with keeping both picks if:
They waive Pau (not even stretching him, just keeping the 6.7M on the books next year)
Pick up options on White, Murray & Poeltl
Renounce all free agents which is really Rudy, Dante & Quincy
Trade Mills with taking nothing back.
That would leave LMA, DeRozan, Bertans, Beli, Forbes, Poeltl, Lonnie, Murray, White & Metu (10) players, with 2 first round picks (SA’s and TOR’s) and 15M in cap space. So SA would have to think that they could replace Rudy, Mills & Pau with 15M & 2 1st round picks which may be tough to do.