Generally speaking, in PR 1st Person Weapon Models (ie, the model the player is holding, not the model you see other players holding) is around 8k tris, never should be much more than 10k at a push and that's with a lot of attachments.
Here is PR's 1p model for the AKM, with folding stock like yours and it's 6.3k tris.
As Rabbit said thou, many 1p models have "High Poly" models that are like 50k tris and are used to bake high poly normals and AO etc from to their texture.
3rd Person Weapon Models should have a lot less detail than that again, although many of PR's 3P weapon models are just clones of 1p and not very well optimized, but really they should only be a few fousand tris at most for their LOD0.
The Bren is a good example of how a weapon for PR should be like:
1st Person LOD0:
3rd Person LOD0:
3rd Person LOD1:
3rd Person LOD2:
3rd Person LOD3:
