It really depends on the type of MDU system that was installed in your building. Many of the early MDU systems did have a 10Mbs limit. The current MDU systems can handle up to 20Mbs. There will really be two questions. Does your building have one of the older MDU's (this would have been installed about 2.5 years ago or longer). The second question would be, is the wiring in your building modern enough to handle the higher speeds. The second is actually the more important questions. If the wireing in the building can handle it and you have an older MDU, then you (and your neighbors) would need to request a modern MDU. If the answer is no, then it doesnt matter what the MDU is, your building would need to upgrade the wiring first.
When the service is installed, the engineers who planned and set up your building would likely have put in a limit so that when the billing/order reps pull up your acct, it shows that only 10 is available. So even though technically MDU's can handle a faster speed, your actual building is limited to 10 in their systems. Remember that the sales people are not technical, they can only tell you what their screen says. They dont understand the technical details of the service.
You also may want to request that they have an engineer come out and inspect the building to see what they can and cannot do. You may not get anywhere with this, but it cant hurt to try.