Change amount of triangles drawn without new array.

Hi! I made my own batching system, due to GC lag spikes I'm trying to reuse as much memory as possible, is there a way to change the amount of triangles that are drawn without having to recreate triangles array? Like doing some copying and telling unity that x last triangle indexes are not being used. I know in opengl you specify how many triangles you want to draw from an array so maybe unity has this option too.