Having just a few such meshes might actually be fine. Luna will do its best to apply appropriate compression to save on both wire size and startup time, so try running the build on target devices first before amending the mesh.
Big mesh usage, this might significantly increase output files size.
Luna warns developers each time it encounters a mesh in use which is over 1Mb in size. In some cases, having such a sizeable mesh is fine, but for many instances (Playable Ads, Messenger Games etc) this might be a problem due to the impact on the build size. In addition to that, having a mesh collider using such a mesh will incur additional performance penalty as Physics engine will have to process each and every vertex at startup.
Steps to fix
Try using a simplier mesh geometry, or even employ techniques like Bump Mapping to keep the level of detail at acceptable level.