I made a cold start test connecting the GPS module to the computer using the onboard USB connector. The u-center software immediately recognizes the module and starts to display the GPS data.
In this test the antenna doesn't have a full view of the sky because it is positioned on the window sill and the wall of the house is blocking the South portion of the sky. This is clearly visible from the Satellite Position View in the u-center map, only the upper half of the map shows the visible satellites. Despite the non-optimal position, 30 seconds for the cold start is pretty good.
The design of the board can be improved a lot, I made some mistakes calculating the RF trace impedence and some other mistakes caused by my little experience in PCB design. U-blox did a great job with this module that seems to be very tolerant to noob mistakes.
The test was made using this active antenna.