Lubuntu does not provide what you’re asking for, as stated in this blog
we will no longer provide minimum system requirements
The requirements will vary on a number of things, including how often you apply security fixes (users who do it less often need more disk space when upgrades accrue), whether or not they’ll be adding additional software to their system (this will need space, and the types of packages added also impacts space required) and a myriad of other items such as will they want to release-upgrade to a later release (as this will require substantial free disk space) or as many bloggers prefer just nuke & install which of course needs less.
We all use our systems differently, and thus what we consider minimum requirements will vary too.