It’s more likely, I think, that you simply have too many meshes.
You see, a major limiter for modern graphics cards, as I understand it, is not the polygon count–as we know, that ceiling is quite high these days. Instead, it’s the batch count: the number of separate “chunks” that the card can handle at once.
Thus, given the same number of polygons, it may sometimes be better to have those polygons be held in a smaller number of meshes than to have them spread across many meshes. That said, this isn’t a hard-and-fast rule–sometimes it better to aid culling by breaking things up, or to find a balance between the two.
From what I gather, it’s generally best to have no more than a few hundred individual meshes.