I have to create a webmapping interface for slow internet connections. I thought on creating the mbtiles and unzip them on their server (mbutil), but I am afraid they don't have quite a lot of disk space there.
The question is, it is possible to directly read the mbtiles? if yes, what about performance?
Yes, you can do this. For Node.js, look into something like node-sqlite. Performance can be limited by concurrent reads, but it all depends on what kind of traffic you are expecting. But Mapbox actually ran on this sort of model early on (see TileStream), before growing in size and traffic demands.