Although I'm not a tile installer, I think you will have some problems with both the mastic glue and grout sticking to a painted concrete floor. Adhesion problems will be worse with glossy hard epoxy.
At the very least the floor should be roughened with 36 grit or coarser sand paper. Visit your local tile dealer or talk to a tile installer about additional preparation steps before installing your tile. A special glue could be available that will address this problem.