Lol there's a second currency block a few levels later- after you've spent your 15000 you have to purchase 2 coffers, except the missions have only given you 8-9k worth since the spend 15000 mission, and previous purchases don't count. At least you have more rooms unlocked so this one will only take a day or so to grind out, but still, on a 7 day event anything that stalls like that is burning time, plus it's another day you can't make the rankings.
Speaking of rankings, does anyone know are we actually ranked against other players? I find it very odd that the top players always score roughly 50k and build it up evenly throughout the 24 hour period- including on the first day when all f2p players can't be doing anything at all because of the first paywall.