While it could be a good solution, a new deck and torchon covering might not necessarily be the best solution. Without knowing more about the roof, it's hard to say for sure, but metal roofs are certainly capable of suitably covering on a low pitch.
As an alternative solutuion, I'd suggest that a single-sheet rubber (EPDM) or glass fibre reinforced plastic roof would be less likely to develop future issues than a torchon felt roof.
Unless the existing roof is seriously deteriorated or compromised, there are several options for repairing a roof. It could be that the roofers you have approached so far have more experience with torchon (it's easy) or to re-lay the roof would be more profitable for them than to repair the existing roof. (Cynical, yes, but having experienced some areas of the construction industry, entirely possible.)
Is the leak on the edge of the roof or in the centre? An edge leak could indicate a flashing problem rather than a roof problem. Are there any penetrations (pipes, ducts, etc) through the roof near the leak?
Also bear in mind that flat / low pitch roofs can show the water on the inside some distance from where the actual leak is.
Is there even a leak? Have you ruled out that it's not a condensation issue? If warm, moist air is getting past insulation and hitting cold metal, you will get water dripping, which will appear as a leak.