We've tested this on 2f2f extensively with 15v15. There was only one instance in which BLU made it to the 3rd stage, so I can't comment on that stage yet.
In Stage 1, it's very easy for RED to control the gated passageway to the point where it's useless for BLU. The presence of the medium health and ammo kits at the top allows a single RED demo to completely control that area. The balcony itself is completely exposed to the full breadth of the second CP area and is vulnerable to snipers, stickies being randomly lobbed up from below, etc. At the very least, I'd recommend moving the health/ammo kits to inside the tunnel or behind the gate, where only BLU can access it easily. Secondly, I'd recommend more cover for RED. A sniper in the alcove on the opposite side can contribute to making it completely useless for BLU. One idea is shown here:
The passageway on the opposite side is a bit too narrow and is prone to being camped easily by RED. I'd suggest expanding it:
Stage 2's second capture area is in dire need of attention. Because this area...
...is typically a zone of death for BLU, RED is too easily able to flank BLU by means of the stairs. The height advantage RED has in the large indoor area those stairs lead to (with the catwalk) is difficult for BLU to counter because of the lack of visibility on BLU's side. I'm not sure what the best remedy is for that area.
The upper tunnel is almost useless for BLU. The length of the approach to the exit is too long and too vulnerable to snipers. You're forced to walk a good 10-15' towards snipers with no cover. IMO, the tunnel approach should ideally allow BLU to counter sentries and defenders on the platform overlooking the "death zone" highlighted earlier. However, the placement of the rock to BLU's right negates that purpose. I'd recommend looking into realigning the upper tunnel exit so it is not parallel to the direction RED travels. Here's one idea: