I haven't seen this phrase before but based on your description of the context, it appears that the meaning is based on the process of "shipping a release of software" (back in the day, software was released on physical media and so one had to ship the physical media to distributors). Software is released in Major Releases (Version X), Minor Releases (X.Y) with follow-up minor patches (X.Y.Z) that provide bug fixes and performance improvements. The phrase "it's not fully shipped until it's fast!" suggests that the software developers adopt the strategy of shipping an initial release that is not as fast as they think it should be and then follow up that initial release with follow-up patches that improve performance until the software is (in their opinion) "fast".